Updates on the aRocket discussion list group project.

The aRocketWiki has a section on the igniter, the aRocketIgniter.

Andrew Case has put a page up on his igniter progress

Duncan McDonald has a section on the RocketWork Bench site at Sourceforge.net and is blogging his progress there.

The aRocket group has begun work on a reusable open source ignitor design. Here are the updates posted to the aRocket listserv:

Update posted Oct. 13, 2003 by Dr. Case

I did a cold flow test on the igniter injector system this weekend. I substituted water for IPA and nitrogen for GOX. This was also a test of the propellant pressurization system, in particular the little widget I made to adapt a paintball tank to serve as an IPA tank (picture here , schematic here) . The adapter worked perfectly - no leaks. There were leaks elsewhere in the system due to my not using thread dope on the NPT fittings. I knew I was taking a chance doing this, but figured I could always fix it if it turned out to be a problem. It did, and I will. The notion of firing the igniter with little puddles of IPA lying around does not appeal to me.

Currently all the plumbing is NPT and swagelok. I'm going to ditch the swagelok and go to AN fittings at some time in the not too distant future, but probably only after I have a successful hot fire test.

The spray pattern was uniform as far as I could tell by eye. I bought a disposable camera to take a few pictures, but I don't have great hopes for high quality from them. I'll have to get them developed and scan them before posting them on rocketforge. Next time I'll remember to bring the digital camera and get some high quality shots. The test ended when a little water from one of the leaks got into the electronics and caused a solenoid to lock up in the open position. I don't think any damage was done that can't be fixed by drying everything out.

The only remaining steps before hot fire are to reconfigure the plumbing and to oxidizer clean the GOX regulator. I probably won't be able to do it before the end of the month due to an upcoming conference, but shortly after I get back it will be my top priority.

Udate posted Oct. 11 2003 by Duncan McDonald

Here's the text version. The html version with linked references and a block diagram are at SourceForge.

In September I thought I was pretty close to getting a board done. Jamie Morken volunteered to write the microcontroller code and after we went over everything Jamie pointed out I needed a couple of more I/O pins on the AVR (a 32 pin ATmega8). After trying a few workarounds it was clear that I would have to switch to a 44 pin Atmega16.

Since I was faced with that setback I decided to build a small prototype of the AVR microcontroller circuit and check out the noise situation that I was so worried about last month. I also learned how to use interrupts and use the AVR onboard timers so it was a fun little project.

I didn't bother to write all the code (or get Jamie to do it) and just set up the 16 bit timer1 to put out a 1kHz square wave. Once the timer is programmed it runs independently of any other code that is running so it is like mini-multitasking in the microcontroller.

To imitate the other code (for solenoid control, ignition detection, etc.) that will be running in the main loop I programmed two output pins to drive two LED's that blinked in an on/off sequence. That way it would be easy to tell if the AVR died or freaked out when the spark plug was sparking. Well, the square wave came out and the spark plug sparked , but the LED's went wacky.

When I removed the coil 12V (oh yeah, I used the old sparkplug/coil prototype Thom and I had used before except the coil and plug are rigidly mounted to a small aluminum plate. The coil is connected to a large 12V gel cell and the controller to a 9V battery), the microcontroller went right into the main loop like nothing had ever happened. If there was a lot of EMI I would expect the program counter and register contents to be scrambled and the whole thing would just hang.

Somehow the controller was able to recover quite nicely! Obviously there is some kind of EMI issue that needs to be solved so I am first going to try adding a snubber on the IGBT to reduce the flyback dV/dt, second I'll shield the coil/plug and/or processor, then third add optical isolation to the driver and isolated power if absolutely necessary.

To design the snubber I really need to know what the coil HV waveforms look like so I need a HV scope probe. I have been avoiding this issue since HV scope probes are kind of expensive ($300-$600). I found a few used ones on Ebay for about $100 but decided to try and build one first. There is a nice explanation and example at Basics of High Voltage Probe Design and Homemade High Voltage Probe. I wasn't able to find any of the required high voltage resistors at the usual online sources so I called Caddock directly. I talked to a very friendly applications engineer who recommended the MX440 11kV 10Meg resistors as a place to start. When I asked for one sample he replied "I won't send you one but I will send you two. I never send one of anything". Nice guy! It will be interesting to measure the actual output voltage as I really have little idea of what it is.

On another note, as I mentioned in another Arocket post, I was fortunate enough to see Elon Musk of RocketX speak at Stanford University. In the course of his talk he mentioned that they were using ethernet for internal communications, which got me thinking. I had bought an AVR ethernet demo board from EDTP Electronics for another project ( Easy Ethernet AVR ). The EDTP board comes with C source code for an ImageCraft compiler. There is also source code for the free AVR Freaks gcc compiler (which Jamie plans on using for the igniter board) elsewhere on the 'net. I have a CodeVision compiler and didn't want to take the time to install the gcc compiler ( Winavr ). Fortunately it only took a few minutes to fix the compiler errors and produce working code (well, I was able to ping it) using my CodeVision compiler. A pretty complete solution (support for tcp, udp, icmp, arp) fits in only 5KBytes out of 16KBytes of flash memory. Pretty impressive! And that 5K includes some UART code for debug messages so I bet it could be reduced to only 3 or 4K for tcp support only. The ethernet controller (Realtek RTL8019AS) is also only $8. If CAN turns out to be a big hassle, ethernet looks like a pretty attractive alternative.

Update posted Sep. 6, 2003 by Dr. Case:

After a summer slow down, this igniter project is moving again. I am currently laying out the PC board and hope to send it out this weekend. I 'm using Eagle sw and have found that I have to make my own layout packages for library parts 90% of the time. That really slows the process down. I am also a bit nervous about induced noise from the coils primary voltage flyback causing the microcontroller to reset. I am going to set up a little experiment to test that this weekend as well before I send the PCB out for manufacturing. BTW, I have been using CustomPCB in Malaysia for board manufacturing lately. $72 gets you a double sided, 4" x 5.5", solder masked and panelized (they cut up the 4x5.5 panel into as many of your pieces as fit) fedex'd to your door 5 business days after ordering. Much better than ExpressPCB or Olimex. The owner, Gary Cho, has been very helpful and responsive to all of my questions. A global economy success story. One issue I had on the PCB was heatsinking the surface mount coil driver (the board is almost all surface mount). There are a lot fewer heatsinking options in SMD than through-hole. I talked to an applications engineer at Aavid/Thermalloy and he recommended a heatsink that should do the job. I hope.

Thom McGaffey and I had worked on machining the igniter body about a month ago but the original design was too hard to accurately machine. Thom redid the design and has machined and welded a beautiful prototype from 304 stainless. I didn't get a picture of it but I will next time.

Decided to use the Tecumseh small engine coil. It is not as high performance as the Ford coil and it runs hotter, but it is $18 versus about $60 and has a nicer form factor.

I have been talking to the guys at Portland Aerospace (PSAS) about their use of the CAN bus as I am designing in both CAN and I2C (and manual bit switching) interfaces. I hope to meet up with them at BALLS and get an up close look at their avionics architecture & implementation. They will be launching their airframe with both an N and O motor at BALLS.

I've put some pictures and schematics on rocketforge.
The Paintball bottles
The adapter fitting
The fitting on a bottle (out of focus - sorry about that)
Plan for the adapter
IPA Plumbing layout

Update for July 30, 2003 posted by Dr. Case

It's been a slow couple of weeks.

The main accomplishments since last update have been scrounging well over 100 feet of Unistrut in useful lengths along with connection hardware, and designing an IPA tank. This is more than enough to build a good mobile test stand and still have quite a bit left over. I hope to start construction of the test stand in the next week or so.

I've settled on a home made tank for the IPA, since that's the simplest and most flexible course. The tank will consist of a 12 inch long aluminum tube, ID 2.5", OD 3" capped on each end by a 1/2" thick 2.5" diameter aluminum endcap sealed with O-rings. The endcaps will be held in place by 6 screws passing radially through the cylinder wall into tapped holes in the endcaps. The O-rings grooves will be cut into the endcaps close to the inside face, so the retaining bolt holes will be outside the pressurized section. The screws will be either #10 coarse thread or 1/4-20, to be decided when I do the shear strength calculations (I prefer the smaller size, but I want plenty of margin). I'll probably make three endcaps while I'm at it so that if I decide to change fittings I can just drill and tap the spare (blank) endcap instead of having to go through the whole setup procedure for turning O-ring grooves and tapping bolt holes.

Relevant peak stress calculations, using a tank pressure p = 450 psi (formulas from Machinery's Handbook):

Cylinder section (D = ID = 2.5", t = wall thickness = 0.25")

s = D*p/(2*t) = 2250 psi

Endcaps (R = radius = 1.25", T = thickness = 0.5")

s = 0.39*pi*p*(R/T)^2 = 3446 psi

Since even untempered 6061 aluminum has a yield strength of 8000 psi, there is plenty of safety factor, especially since I'll most likely be using 6061-T6, with a yield strength of 40,000 psi. It's interesting that even a small, thick flat endcap sees such a large peak stress. Clearly this will not scale up well.

I got a paintball regulator off eBay for ~$35 that's adjustable between 300 and 1000 psi output, but it needs <1200 psi in, so I'll probably go with CO2 for pressurization initially, using a bottom of the line paintball tank, unless something better shows up. There are Nitrogen tanks on eBay with high pressure regulators for ~$150, but I'd like to see if I can do it cheaper than that.

The AVR microcontroller is turning out to be a bit more of a PITA than I had anticipated. The Olimex board doesn't come with a power supply and the power plug is not a US standard size AFAICT, so I'm going to have to do a little soldering to replace the connector with something that works with the Radio Shack power supply I have. On the plus side, one of the guys I work with turns out to be a secret space geek, and he's also an EE, so he's offered to pitch in. Should be a big help

......Andrew

Posted June 28, 2003 by Duncan McDonald

Did some more testing of the coil/sparkplug yesterday. Put some thermal goop on the heatsink which kept the mosfet cooler. Just used the Ford "coil on plug" as it has the best performance of all the coils tested. It is interesting that all the other coils had turns ratios of about 50 whereas the Ford unit had a turns ratio of almost 70. That combined with a 38mH magnetizing inductance makes this one a winner. Now I just have to find the Ford part number and how much it costs. Played around with the two best spark plugs from last time, the BM6F and the 10mm NGK racing plug. Somehow the racing plug didn't seem quite as impressive as it did the first time we tried it. Still produced a very hot spark, but it was more or less the same as the BM6F. The racing plug has a drawback of a 3/4" threaded barrel ("reach" in sparkplug nomenclature) but not having a protruding electrode should help avoid any potential fouling issues. As a result we decided to go with the NGK plug. It's less than $3 so it is certainly cost effective. Tried various duty-cycles and found a range of 40 to 60% would work. 60% gave a bit hotter spark, 40% a bit weaker. At 10% it was extinguished or close to it. 1KHz was the best overall frequency so we decided to just go with 1KHz and 50% duty cycle.

Worked through the preliminary design of the controller board. It will have something for everybody (at least the prototype): AVR controller, CAN bus interface or parallel control lines, two channel temperature sensing (chamber and heatsink), two channel solenoid control, status readback via the AVR or parallel lines. Should have boards in two weeks. Question though: are there strong preferences for SMD or through-hole? Either will work and through-hole may have some advantage because it is easier to heatsink through-hole devices. But it will be smaller with SMD. Any opinions?

Thom has a design for the chamber and is starting on that. It'll be GOX and Hydrogen. The prototype will have outboard gas regulation so we can easily change pressure. The body will be a chunk of stainless steel with diffusion welded SS tubing to the gas ports. Holley solenoids for gas control. Looking at reusing large threaded CO2 cartridges as the flight gas storage. Will start testing the prototype chamber a week from Monday (July 7).

So far so good!

Duncan

Posted June 24, 2003 by Dr. Case

I just got the regulator I ordered from Aerocon. Looks good, if a bit larger than I expected. It looks like cleaning it for Oxygen service won't be too hard, though I haven't taken it apart yet. That will have to wait until I can get it to a cleaner environment - no point in stripping it until I'm ready to clean and put it straight into a clean, dry ziploc bag.

It needs gauges and fittings, which I bought from McMaster-Carr. Interestingly enough, despite the fact that it's easy to pay upwards of a hundred bucks for gauges, McMaster offers Oxygen cleaned high pressure gauges for under $12 a pop - I bought two, a 4000 psi one (part # 32255K77) for the high pressure side and a 1000 psi (part # 32255K84) for the outlet. The gauges are good to only 3% midscale (which means probably at least 5% at the ends of the scale), but 3% is good enough.

Posted June 16, 2003 by Dr. Case.

I've pretty much finished the igniter body and injectors. The only work that still needs to be done is a little tidying of a burr on the Isopropyl injector and fitting a plug to the ignition detection port. Once I've fired successfully I'll start work on ignition detection, but for now I'm just going to blank off the port.

There are a couple of imperfections in the injectors and body, all of them due to thinking while standing in front of the milling machine. Never do this. Think at the desk, machine at the mill. I relearn this lesson about once every ten months or so. Redesign on the fly as you are making a part is just not smart. As it turns out the imperfections have no functional implications, but it's irritating to put so much effort into planning only to make simple errors.

I've ordered a regulator for the GOX, Aqua Environment model 415-1500 from Aerocon Systems. Price was $260 including S&H. It's not O₂ cleaned, but I can do that myself. Also ordered a Lake Axial Flow solenoid, which is actually for another project but might get used on the igniter depending on how things work out.

I posted last week about the conical end mills from Conical Tool. They've arrived, and they look like just the ticket for the job. The smallest has a tip diameter of 1/32" - very small and delicate looking.

Once the regulator arrives the remaining items before test firing are: machine a mount for the igniter find a suitable tank for the IPA design and build a mount for the IPA tank decide on IPA pressurization system and implement it hook up plumbing sort out electronics

The last item may turn out to be trivial if I just use the preexisting circuit from my previous effort. This may be the best approach, since the using the AVR board requires some on-board construction and learning to program in either AVR assembler or c. Once I'm confident of the other parts I can tackle the microcontroller and associated circuitry. IPA pressurization is likely to be via something cobbled together from paintball gun parts.

Date: Thu, 29 May 2003

From: Duncan McDonald

Can't say I got a whole lot done last week. This week is heading in the same direction. I did get together with Thom McGaffey and remeasured the coils DC resistances. Thom has a 6 1/2 digit voltmeter and figured out how to set up 100 power line cycle integration for stable low resistance measurements. The new measurements confirm the previous set: on an automotive coil the primary + terminal is the common connection for the HV secondary. I received my parts from Digikey so I will try and build a breadboard of the coil driver this week. Like Andrew, I have had my eye on the CM6 10mm sparkplug. Bill Bullock came up with a fantastic website http://www.sparkplugs.com/. Click on "Advanced Tuners and Engine Builders Data" and there is complete parametric selection. Check out the 10mm racing-style plugs for $2.29 http://www.sparkplugs.com/more_info.asp?AAIA=&pid=3315.

Date: Wed, 28 May 2003

From: Andrew Case

I was ill all of memorial day weekend, so the expected burst of productivity never materialized. What I did get done was finalizing the injector design and locating some sources of information on GOX handling. I just received a copy of Vance Harlow's Oxygen Hacker's Companion, which is actually for divers, but contains lots of useful information, particularly for people planning to reuse diving gear in nontraditional ways :-)

I received the spark plugs I ordered, NGK CM-6 10mm spark plugs. They are really small, so I'm glad I didn't go for the 8mm size. These are on the borderline of getting finnicky to handle. One unfortunate discovery is that the threads are 10mm by 1mm pitch, so the hole I tapped 10X1.5 is going to be drilled out and tapped 1/4 NPT for the ignition detection, and a new hole drilled and tapped 10X1 for the spark plug.

This week's plan is to build the injector head and start familiarization with the AVR.

Date: Tue, 20 May 2003

From: Andrew Case

I'd designed the new igniter body, and built most of it. Still to do are a tapped port for the ignition detection and four tapped holes to hold on the head end. I've got numbers and a rough design for the injectors, nominally using GOX/IPA. One immediate insight from the injector design is that the holes are really small, and will be a major PITA to machine. I'm working on refinements of the head end and injectors to set things up so that the tricky machining is spread out over multiple pieces, and there is no tricky stuff that has to be done right at the end of a whole bunch of machining. This is to try to minimize the probability of investing huge amounts of time in the piece only to blow it on some finicky but critical detail. If I'm going to mess up I want to do it early, so I can start over with minimal waste of time. Also I think I have found a way to finesse things so that I can cut and try on the Oxidizer injector.

I'm going to double check my calculations tonight and I'll post calculations and dimensions tomorrow unless something comes up.

The AVR board, programmer, and chip are now in my hands, and waiting for me to have some time to work on learning a little about microcontrollers and programming them. Jamie Morken has sent me some sample code to look at. If things go smoothly with the injector design and construction (ha!) I'll start looking at the microcontrollers this weekend. I'm guessing the injectors are going to be a bit of a production to do, though. I also have Mike Castle's PIC board waiting for me to take a look at it. I'll do that in parallel with the AVR.

Date: Tue, 19 May 2003

From: Duncan McDonald

(You'll have to go over to http://rocketworkbench.sourceforge.net/projects.phtml to get the files referenced below. The reports will be blogged there as well.)

I went over to a company owned by some friends of mine (Amicronix Test Systems) that has a small metrology lab. They have an HP 3458A 8 digit voltmeter that will resolve 10 micro ohms. I hadn't received the mosfets from Digikey so I couldn't take the inductance meaasurements. I settled for taking the equivalent series resistance (ESL) measurements of the coils primaries and secondaries and measuring the coil turns ratios. I first measured the turns ratios by driving the primary with a small (40mV to 250mV) sine wave and measuring the secondary peak-to-peak voltage. There was a lot of "smear" on the low voltage waveform that made the measurement difficult. I then tried a higher voltage of 1Vp-p on the primary and measured the secondary again. These "high drive" measurements came out much better. I recorded the voltages and the respective phases in the attached spreadsheet. The phase gives the "dotted" sense of the terminals. Transformeers are notated with dots on the windings to show the relative phase of one end of each winding. As I expected, the secondary (high voltage lead) was in phase with the "+" side of the primary on the two coils that had a marked polarity.

Next, I measured the primary and secondary ESR's using a four-wire kelvin connection. I was able to decently resolve 1 milli ohm, but below that the measurements were a little noisy. The HP 4184 has the provision to increase the ADC integration time, but I couldn't figure out the menu system. I also couldn't find the manual (almost everyone had already left for the day). On a whim, I decided to measure the secondary with respect to both ends of the primary (+ and -). The secondary impedance was always higher with respect to the "minus" side of the primary than the "plus" side! I was surprised, because that means the + side is the common point with the secondary, just the opposite of what I would have thought (see attached schematic). To read the schematic you'll have to download the viewer from ExpressPCB. I seem to recall that automotive sparkplugs fire when the electrode is negative so electrons flow from the center electrode to the rim. Is that correct? If so, this picture is consistant with that scenario. But also if this is true, I should really redo the turns ratio measurements as I may have been driving the coil in such a way as to bias the secondary with the primaries drive level. It's a small error, but should be corrected.

I am not 100% sure of my results because of the noise problem I had with the voltmeter. Because of the noise I really only had 4 significant digits. I need at least one more to really be sure of these results. To reduce noise I either have to average some samples or increase the integration time (the voltmeter has a dual slope integration converter). I couldn't figure out how to do that by just fiddeling around, I need to read the manual. Unfortunately Amicronix just sent the meter out for calibration so I can't use it again for a couple of weeks. Thom has a 6 and a half digit voltmeter so I am going to go over to his house on Wednesday and try again. If the IGBT's come in we can also do some inductance testing. Thom also reports he received the thermocouples for ignition detection.

I would also like to get some pictures posted this week!

Date: Tue, 6 May 2003

From: Duncan McDonald

I came across this technique for non-optical ignition detection that apparently is used in "smart engines". During the portion of the ignition cycle when there is no spark, ie when the coil is charging, place 400V across the plug spark gap and see if about 1mA of current flows due to gas ionization. That does require some pretty heavy duty diodes to keep the HV out of the 400V supply. But how about having a second spark plug that just does ignition detection? There is still the matter of a 400V supply, but an LT3420 would do nicely.

See http://www.fs.isy.liu.se/~larer/Projects/main.html And http://www.hut.fi/~vvartiov/ion/DIY-Ion-Sensing-2.pdf. Clever use of a current mirror for current sensing. Note that the current mirror is drawn incorrectly. The BF421's are PNP transistors.

Seems a little complicated, but in the long run maybe it is simpler than trying to create an optical window into the combustion chamber. What do you guys think?

Date: Tue, 5 May 2003

From: Andrew Case

I just uploaded some PIC code to the arocket uploads area. This code was written by Mike Castle to sequence valves and run the spark using a PIC microcontroller. The file is MCPICign.txt.

I haven't run it, but I will when I get set up to do PIC stuff. I'll report results to the list.

Date: Mon, 4 May 2003

From: Andrew Case

First the controller: I've ordered the programming cable and prototyping board (available through the Olimex distributor in the US at www.sparkfun.com) along with an ATmega8 chip to populate the board. Should be arriving sometime this week. Also Mike Castle in the UK has a PIC board that he's offered to send me (along with some extras for distribution), so we can have a shootout :-) In fact I think I'll probably settle on the AVR, but if we can get a PIC variant running, the more the merrier - the fact that there are some extra free boards lowers the entry barrier for people who want to build whatever we come up with (this is important since the more people building hardware the more thorough the debugging will be).

Ignition detection: I wasn't able to find a photodiode since I couldn't get to my regular electronics supplier before they closed, so I went to radio shack and picked up a phototransistor and a photoresistor. I set them up one at a time on my existing igniter, with the propellants off - just testing if I can see a spark. The bad news is that the electrical pickup from the spark line dominates the signal on both. This isn't all that surprising since I had big loops of wire everywhere. Obviously optical detection will require a bit of finesse, if it works at all. I'll try again down the line, probably with a photodiode and better shielding. It's going to require a bit of effort, and it's not on the critical path, so I'm not going to put a really high priority on it.

Date: Sun, 3 May 2003

From: Andrew Case

I just toasted another 555 due to lousy fit of a component carrier in a socket. I'm considering replacing the sockets, but perhaps it's time to go to a better system. The problem I have with the various microcontroller suggestions so far is price. All the ones I've looked at closely have expensive programming hardware. That need not be a huge obstacle since there are presumably people willing to rent out the use of their hardware, but that takes time. I need to be back on the air by next weekend at the latest, so I need a COTS solution.

I found a possibile solution in the Basic Stamp: . It's only $79 for the bottom end of the line, including programming software, manual, and cable. Memory holds only 80 instructions, but the application is simple. There's also a little space for interface electronics. One nice thing is that it runs directly off a 9 Volt battery, though power can be 6-15 Volts. If you torch the chip, replacements are only $34. The chip executes ~2000 instructions per second, and it loops continuously through the code in memory, so even if you use the full 80 instructions you're looking at executing the whole loop every 40 milliseconds, which is fast enough. In practice you only need to check the status of the ON switch and the ignition detector, and sequence the valves in the right order, so you ought to be using only 40 instructions.

Questions: Is there a catch somewhere with using the Basic Stamp? Are there other cheap, simple, ready-to-go microcontrollers?

Date: Thu, 1 May 2003

From: John Carmack

XCOR uses a programmable industrial sequencer to run their igniter, but I, of course, wrote a computer program to control it from a laptop.

I use the parallel port for input and actuation (I use a little public domain driver to allow this under Win2K / WinXP, like it used to be allowed in Win9X).

bit 0: igniter gox bit 1: igniter fuel bit 2: main propellant oxidizer bit 3: main propellant fuel bit 4: igniter spark (the computer toggles this, so it doesn't need any extra timer circuitry) paper out input signal: igniter chamber pressure switch

Our current setup is slightly different, because we have hacked up one of our old vehicle driver boards to do this, but we are probably going to build a nice new board that includes two bi-directional motor drives so we can control our big servo valves with the same board. Russ is also looking into building the spark generation hardware directly, instead of using the MSD equipment. Russ's company makes some stun gun type hardware as well as radio hardware.

I am going to integrate support for dataq serial logging this weekend, so it will be a nice, self-contained little program like our old test stand program.

I will make this source code public domain for the igniter project after we get everything tested and cleaned up a bit. The drive board for this will probably cost a few hundred dollars for all the solid state relays and such, but we can probably offer the layout and parts list to the project.

Date: Thu, 1 May 2003

From: Andrew Case

I got a quote from Acra-Ball on glass balls at less than 2 bucks each - very reasonable, except the minimum order is $100. I'm trying other options for a viewport.

Pierce reminded me that XCOR used Ethane for their teacart engine - self pressurizing to ~540 psi, nontoxic, pretty nice stuff. Why don't more people use it? - Roberts Oxygen (a local gas supplier) just quoted me ~$200 for a three pound bottle. That's why :-(

Still, it might be worth it for debugging and perhaps for use in small quantities such as for lighting hybrids. I'll talk to SWMBO about financial priorities. Maybe it's time to invest in a regulator and a pressurizing system and just go straight to Isopropanol.

Date: Thu, 1 May 2003

From: Andrew Case

For people working on electronics boards who might be interested in having me test them on my system, here are the magic numbers:

I currently switch my solenoids with 7.4 Volts from a rechargeable battery, so the switching pulses to the transistors need to be at least 7.4 V. My present controller uses 9V and that works fine. The timing sequence is: Spark train starts simultaneous with opening the oxidizer valve, followed 0.1 seconds later by opening the fuel valve. Spark frequency is 500 Hz.

Ignition detection is a complicated issue, best handled separately. I can provide a 5V signal that goes high when ignition is detected.

Right now I can test with either a full HV system, or with something that just gives a pulse train out. Since I have an MSD ignition I'll just pass the pulse train to the ignition module (which is what I'm doing now).

If need be I can cobble together something to translate 5V pulses into voltages which are more useful to me.

Date: Wed, 30 Apr 2003

From: Duncan McDonald

I'm about ready to start doing some work on the high voltage portion of the igniter and I'm thinking about two versions: a dumb version and a smart one. They could probably be the same PCB, just more parts stuffed in the smart one. The dumb version has a two pin input connector so that when you apply a logic one (+5V), the igniter starts producing HV. In the smart one there is a comm link and processor that receives a command like "$ignition1 on". The processor then starts the HV. The smart version could have some options like measure HV current flow and HV voltage produced, igniter gas valve sequencing, etc.

-Any particular coil that is small and inexpensive? The Fiero one mentioned is $45- 50. -Seems like 0.030 is a pretty common plug gap which translates to about 17kV, so the coil output should be 20-25kV min. -9V to 12V input voltage to the board. -For the smart version, what should the comm protocol be? TCP/IP or UDP/IP? That seems kind of complicated, but the additional stack code bumps up the processor requirement to an Atmega123 ($17, based on the stack taking 8 to 16k memory) plus an interface IC like the Cirrus 8900A. So that is maybe $13-$16 more than a bare bones serial link. Not unreasonable. I believe a CAN bus implementation would be a bit less $$ as a less hefty processor is needed but you still need one or two interface IC's.

Thoughts? Other ideas?