1 June 2007
Another month gone. Drove down to Bill Shurvinton today in Hampshire to pick up my megasquirt kit; my next sub-project. Megasquirt is basically a DIY ECU! The ECU can control practically any 4 stroke or 2 stroke engine, both fueling and spark and a lot more besides. Can also connect to the PC via a serial cable and have a play with the settings, re-program, etc.
This is going to be really interesting! It must have been ten years ago when I last picked up a soldering iron. I decided that I would also build the Megasquirt Stimulator which takes the place of a car when testing the ECU on the bench. I decided that I would tackle soldering this first as it is a lot cheaper if I stuff it whilst honing my soldering technique. Plus I also need to get the tempeature controlled soldering right by trial and error and hopefully won't melt the PCB or raise tracks in the process!
Megasquirt stimulator assembly instructions for Version 2.1 can be found here
Photo of the stimulator kit. Very neat all the components bagged and marked up with corresponding markings on the PCB making assmbly a breeze. Went steady, but within 30 minutes it was assembled.
Photo of assembled stimulator below.
2 June 2007
Session 176 - Megasquirt ECU assembly
Having completed the megasquirt stimulator now its time to begin assembly of the main ECU. The assembly instructions can be found here.
I spent three hours on this today. Rather than just go ahead and solder the components in my usual order, i.e. all the resistors, then capacitors, then diodes, then ICs I decided to follow the steps as described from the megasquirt site. Following this method of build up of each ECU sub-system at a time means that you can test the functional operation of each.
Here is a photo of the megasquirt kit. Again all the components are bagged. Be careful though as most bags contain common components but not of the same value for example, resistors and capacitors. It looks a bit daunting doesn't it. But doing a step at time and it will soon be done.
So following the method, the first thing is to complete steps 1 - 23 and this gives you the power supply.
Completing the above steps, the PCB now looks like this:
Pictured with the stim attached. The stim is used to provide a 9v power to the PCB via the DB37 connector. With the power connected the instructions describes various pin outs to test for a +5V against various ground pins. With my digitial meter I registered a +5.03V for all the associated pins, which is really good news! I was fretting a little because failure here could either by the megasquirt or the stimulator as this is untested. Thankfully worked first time. Had it failured there is apparently a detaied diagnostic/analysis method on the megasquirt site, I was going to have a read last night but I thought nah, I shall cross that bridge if I have to.
So with this part of the construction complete and tested as working then I proceeded to execute steps 24 - 26 - Serial communications. Wow, serial communications to the PC. Not many components in this part owing to the dedicated serial communcations IC which performs all the serial communications I guess to R232 specification. However this step requires the PC and installation of a USB - Serial cable convertor and installation of the driver software.
This is a photo of the PCB with serial communications circuit completed:
To test this circuit is a little more exciting as you need to connect to the computer and send some data from a serial communcations package such as Hyperterm. It a bit of an anti-climax because all it does it repeat the data back to you but hey it proves the data has been received and sent back. Decided to call this a day at this point and end on a positive note. I shall continue the efforts tommrow where I hope to actually have something that will process data, maybe!
In my soldering rest periods I have been working on my plenum chamber which is almost as perfect as I want it.
On another note I ordered a crank scraper from the states at a very good price actually as the guy decided to re-design the scaper so that it is a dual scraper specifically for the Rover 4.6 Crank. He email some pictures today before he dropped in to the post. Pictures below.
Can't wait to receive the item and try it.
3 June 2007
Session 177 - Megasuirt ECU assembly..
Today I assembled the clock circuit, steps 27 - 41. At this stage I can now install the CPU of the ECU and connect up to the computer and do things like look at the battery level and the timer. Wow a little bit closer.
Photo showing the ECU connected to the stimulator and serial comms to the PC. By the way my notebook does not have a serial connector, I picked up the cheapest USB-Serial convertor I could find at Maplins (£19 but still a rip off!) and this seems to work with the megasuirt. Just remember to use Comm8 in the megatune software!
Installed Megatune software on the PC which is used to test the communications to the device and perform tuning, etc. This is showing the real time screen. The gauges are not important at the moment as the input sensor circuits are not yet complete. The two reads to check is the timer counts up once a second, at the top left and that the battery voltage is somewhere between 8 and 9 votls. I have made a battery meter!
I have installed Megatune for now as the instructions for testing on based on this version but I do intend on using Megatunix instead. Yes, I prefer the stablility of Linux over windows. Also Bill tells me that Megatunix has a neat GUI!
I also note that one can use a Bluetooth device in order to facilitate comms with PC, like the sound of that. You can get a serial to bluetooth adaptor but it has to be an inteligent one not one that does not need windows drivers in order to work, this may come as a surprise but megasquirt does not use windows (thank goodness, that would bring a whole new meaning to blue screen of death! which I got just when I unplugged the serial cable)
5 June 2007
Session 178 - Megasuirt ECU assembly..
3 hours on this section.
Right next step is to construct and test the input section. This is covered under steps 42 - 55. Step 50 requires a decision. You need to decide, well actually know the type of tach signal that the megasquirt is to receive from the engine sensor. The main choice is Hall/Optical or VR. Hall/Optical is usually from a distributor (points) or directly off the coil. VR stands for Variable reluctor which is a sensor that reads a signal generated by a trigger wheel, this sensor detects ferrous metal passing by. Trigger wheels usually have teeth precisely the same distance apart on a wheel and one missing tooth which means that TDC can be determined by the ECU.
I am using a Ford EDIS 8 ignition control module.The EDIS system was developed by Ford and is very reliable. Megasquirt can operate without this and drive the coils directly but the EDIS unit is completely sealed and water proof and can be installed in the engine bay. Basically the EDIS will run the ignition with no advance without any other electronics other than the VR sensor and the coil packs which provides a limp home fail safe system. Megasquirt will communicate the amount of ignition advance required to the EDIS module. Good eh? Anyway, click here for some more reading if you are interested.
So step 50 you have to decide really if you just want to build a VR circuit or Hall/Optical, well actually you can build both because you can select with jumpers which circuit to use at a later date. I choose to install both which was lucky really because I assumed that I wanted VR and actually I wanted Hall/Optical. Why? you ask if the EDIS system uses a VR sensor! Well this does catch people out I am sure. The VR sensor is the input into the EDIS system and we are going to wire the output from EDIS (PIP) which geenerates a square wave, ie. Hall!.
Another decision was required and this is a mutually exclusive one this time, you have to decide between 50a which is Hall/Optical without coil connection and 50b which is triggering off coil negative.
Next I tested the board in accordance with step 55. Unfortunately it appears that I am receiving no engine speed signal. I decided that I would continue with building the board as I do not know at this point whether the Megastimulator is generating a signal.
6 June 2007
Session 179 - Megasuirt ECU assembly..
I do not have an oscilliscope in order to try and work out if the stim is generating the signal or not. I spent the next 2 hours scrutinised every component as much as I could on both boards and found no immediate concerns. I do suspect the stim is not sending the signal. I am suspecting either the timer chip AD654 and/or switching transistor is at fault.
7 June 2007
Session 180 - Megasuirt ECU assembly..
The next section, you may of guessed is output. Covered in steps 56 - 80, yep a big section took my about 2 hours and that is at an increased pace. Step 65 you have to decided if you need a high current ignition circuit which if you were driving the coils directly you would require. I am using EDIS ignition so do not need this circuit as the megasquirt will signal to the EDIS for ignition timing.
Step 69 another decision, decisions, decisions. This is whether to install a PWM flyback damping and/or standard flyback circuit. Something to do with the type of injectors used, high iow impedance. Low impedance injectors would require damping. Standard rover injectors are low but I have uprated ones which are actually high. I decided to install both circuits.
Step 71, introduces a choice, whether to provide current limit protection to the FETs (14 Amps), not much of a choice in my book, do I want to protect my megasquirt or not! I think I do actually.
That is the main construction complete. Next I need to make some post modifications to the ECU for extra options like tacho output to the dash, specific changes for EDIS8 (just when you thought that is it), knock sensor input, shift lights, collecttive known as MS1 extra these are additional software and/or hardware features. Oh and one more thing, get the MegaStimulator working.
I spoke to Bill (supplier of megasquirt kit) and went through my checks with him and my frustration that I do not really know if the stim is at fault or the megasquirt. He told me that if I cut the tach jumper to the optoin then I could introduce a few manual flickers of RPM at +5v using a fly wire to optoin. Wow, I saw some activity the LEDs light flickered to show injectors firing and megatune showed an engine RPM. So I guess I am right its the stimulator at fault.
Photo of the completed megasquirt V3 board, the blue PCB. As you can see quite densely populated apart from the small rectangular section on the lower left of the CPU and LEDS. This area is the prototyping board, quite neat. The prototyping board will probably attact a few components when I start work on the MS1 extra stuff. The Megastim is the green PCB; much simplier, yet with fault!!
And the underside, the soldering, look at the soldering! The white wire is a jumper from the pin of the CPU that is used to trigger the EDIS module (JS10 to ign). However this will probably be changed because I have learnt that this option may be at the cost of another one and there's a different method to achieve the same result Now this is a real hack, to get the ignition pulse to EDIS you can take the output from the LED that flashes for each ignition event! The back thing you can see is the MAP sensor, this reads air pressure which will be used to ascertain the inlet manifold pressure used in the fuelling calculation.
12 June 2007
I think my MegaStmulator not generating an RPM signal to the Megasquirt is all down to the voltage to frequency convertor chip; AD654NJZ. These chips are not common place, Maplins do not even do any voltage to frequency convertors. RS Components have them in stock so I have ordered two on next day delivery.
As I got my final coat of paint on my plenum chamber pattern last week I smoothed out using rubbing compound and applied the first coat of wax. Wow, mirror finish. Now you can see any slight imperfection in the shaping. You really have to look hard and close to see any, so I think this is the best I can do, I am happy with it. See picture below.
13 June 2007
Session 181- Megasquirt, it lives!
got up at 07:30 this morning to find that my AD654 voltage to frequency convertor chips where on my doormat, wow, service. So as I had alrady soldered an IC socket on my board last night, just a few moments I had my chip installed. Sucess, I was right, the AD654 chip on my board was faulty. Lights everywhere, and I can now rev my simulated car all I want, pity it does not make that V8 sound that I am longing for!
Photo showing the Stimulator flashing away.
Photo of the Megasquirt, also flashing away. Yes I put it in the case.
Photo of the real time display on the PC.
Tonight I undertook to modify the Megasquirt to drive the EDIS8 ignition. If I were to use megasquirt to drive the ignition directly these modifications would not be necessary but I have decided to go the EDIS8 route like many other Rover V8 megasquirts have done. I think I explained the EDIS8 will drive the ignition at 10BTDC with the aid of the crankshaft trigger wheel. EDIS was developed by Ford and a well proven and mass produced system. The megasquirt will take the PIP input from the EDIS8 system and sound out the SAW output to provide ignition advance. As per the diagram below. This also demonstrates the the signal provided to EDIS is VR but the signal into Megasquirt is provided from that and this is a square so Hall/Optical is used as the input in Megasquirt, there, confusion sorted.
Anyway back to the mods in hand, I could have made a simplier mod by using one of the outputs from the megasquirt ECU like some have done but these programmable outputs are few in number and the recommended approach is to make use of the D17 LED which is nearest to the DB9 connector. This LED fires on an ignition event so we can make use of that as an output and save one of the ECU outputs. The instructions for this mod can be found here
I downloaded the latest stable MSnS extra firmware and updated the ECU and then I tested the modification using the megastim and the IGN on the stim now fires up, looks good, however I have now way of knowing it is sequence but it seems to change when I play with the engine speed.
I also cleaned the megastim PCB tonight using flux cleaner and gave a nice coat of laquer all over this basically water proofs the circuit which is actually uncessary for the stim but I intend on giving the megasquirt the same treatment and wanted to try it on the less expensive one first!
22 June 2007
Had a day off work today so spend 3 hours of it working on my plenum mould fabrication, god, very messy stuff!. I have put on several coats of release agent on the pattern and made some weirs to make a split mould as required for this shape. I am expecting to have to fettle the mould a bit and maybe compound it so I decided to do 2 gel coats to give sufficient depth in which to do this. In the end I put around 300g of gel coat on the pattern. I used flow coat which also had white pigment pre-mixed. I left the gel coat for about 90 minutes.
Next I mixed up 200g of resin and applied fine surface tissue and let this go just off tacky. I then mixed another batch of resin, 200g and applied fibre glass to one side of the mould and then mixed another batch of 200g resin and aplied fibre glass (450g stranded matt) to the other side.
I have some useful guides that I have downloaded, you can find them here and here
Photo of plenum chamber mould curing! I forgot to say the plywood weirs I painted with a few coats of PVA release agent.
In case you were wondering, the weir on the front which will form the throttle flange is not actually held on with tape it is screwed down. The weir board going down the centre of the chamber was a little tricky to fix so I used tape around the bench and plastine at the end! Well it didn't move which is the main thing. Now I am anxious for it to cure so that I can peel it off and see the result. I now have to wait five days, this is worse than waiting to unwrap the chrismas presents under the tree. My biggest concern is not being able to release the mould from the pattern or damaging it in the process.
Go to July 2007