[Diy_efi] V2.00 Megasquirt Schematics and Layout

[Bruce Bowling]

All,

I have finished up the next version of MegaSquirt schematics (V2.00), and 
the corresponding layout changes. Everyone go get them (at the same time so 
we can crash the cedant.com web server):

http://www.bgsoflex.com/megasquirt_ShemV2.00.pdf
http://www.bgsoflex.com/megasquirt_LayoutV2.00.pdf

The theme of this upgrade is two-fold - the first and most important is to 
implement circuit changes and modifications which we found useful from the 
cars currently running the MS V1.01 system (we are up to 20 vehicles!). The 
second theme is to make the board a little more flexible for DIY 
modifications, and the eventual addition of ignition.

It is very hard to implement every requested feature in any system. In 
addition, the whole philosophy of the MS system is to be on the extreme 
low-end of the EFI controller spectrum, capability-wise. MegaSquirt will 
run your car/boat/etc., and it will run it well. In addition, the system is 
simple enough for a person to fully grasp what is going on regarding engine 
fuel control, and simple enough to install and tune. However, the system 
will never be a complex system with tons of I/O, etc - there are other 
systems out there (like EFI332 and others) which address this area.

Enough introductionary words - a description of the changes:

Schematic changes:

1) Modification to the tach input circuitry, including the John zener, Wing 
diode, and Ed capacitor. Also, the wattage of R10 was increased to 1/2 watt.

2) Diode D20 was added to prevent the destruction of the fet driver U7 in 
case of accidental power polarity reversal.

3) If you look on the "output" circuit page, you will notice two diodes, 
D6A and D10A. These are alternate diode positions for D6 and D10. These 
diodes prevent the destruction of the FET drivers during injector close due 
to inductive kickback. The two positions allow the kit assembler a choice - 
placing the diodes at D6 and D10 allow current averaging during PWM mode 
current limit, but *may* result in a slower injector close time. The 
alternate placement may allow the injector to close faster, but may result 
in a rougher/spikier current limit waveform on the injector during PWM 
limit. The choice of placement is up to the end user, but a rough guide is 
to place them in the D6 and D10 position if you are going to use the PWM 
current limit mode, or place them in the alternate position if you are 
driving high-impedance injectors. The best thing would be to try both 
positions and let everyone know what you find on your application!

4) On the CPU page, you will notice an addition of a header, JP1. This is 
the much-talked-about header which allows one to plug on another card for 
features such as ignition, etc. This header has +5V, ground, and the SPI 
channel communications lines to the processor (CLK, MOSI, MISO), and three 
empty, non-assigned pins which connect to jumper pads (more on this in a 
minute).  The MS processor is configured as master (via the resistor R14 
pulling up *SS to +5), so any card plugged onto the header needs to be in 
slave mode. Also, everyone grab your pencil and write this down: the board 
[x,y] position of the new header, pin #1, is [2.720, 2.360], where board 
origin is on the lower left of the board (near the LEDS) - you will need 
this if you plan on making your own add-on board.

5) As discussed, it is impossible to accommodate everyone's wants and 
desires for I/O, so what I have done is set up the board such that the 
end-user can configure the board the way they want. Notice on the "CPU" 
page, there are the boxes X0 to X10 all over the place. These are jumper 
pad locations which terminate to a jumper hole on the PCB. These holes 
allow the end-user to wire up the board in any configuration using jumper 
wires. Ports X0 to X5 hook into the port A I/O on the processor - these are 
general-purpose I/O which have the added feature of interrupt capability 
and software-configured pull-up resistors. X6 and X7 hook into the spare 
ADC channels, X8, X9, and X10 come off of the new JP1 header for the CPU 
daughtercard. On the "Connector" page, X11-X14 bring out unused DB-37 pins 
on the output connector. So, there is more than enough user-configured I/O 
to choke a horse! As time goes on, if a particular I/O setup emerges as 
being very popular, then the MS board may evolve to reflect this setup. 
And, for those who may inquire why I did not bring out all unused I/O pins 
on the processor, the reason was due to board layout - these were easy for 
me to accomplish without me having to change the whole board around. If you 
absolutely have to have every I/O port, then you should look at something 
like EFI332.

6) Bootloader entry is now handled by a two-pin header H1, instead of 
shorting a resistor.

7) I left the diodes D1 - D4 on the schematic, even though they are not 
needed. I will indicate on the new BOM that these are there for those who 
do not believe that the processor's internal reverse-diodes provide enough 
protection. Once again, the end-user gets to make the choice.

8) The output FETs will be the insulated plastic-variety.

Layout changes:

1) All of the new components, headers, etc, have been added and routed. In 
addition, some of the troublesome footprint definitions have been tweaked 
to make kit assembly a little easier.

2) All of the new jumper holes are routed to locations easy to get to and 
route (especially for me).

3) The MAP sensor footprint has been fixed, and two mounting holes have 
been added to allow the mounting of the MAP sensor on the underside of the 
board.

We are going to send the board off to the fab house in the next few days, 
and should have it populated and tested within three weeks or so. Once this 
occurs, we will be ready to start the next GB.

To help with the next GB, we are going to institute the following changes:

1) When you sign up to be part of the GB, the web page will compute your 
actual shipping charge. We got hammered with shipping overseas - this was 
totally our own fault for not researching this sufficiently. We have now 
done the proper research and have cost tables for international shipping. 
We will be using priority mail and global priority mail.

2) We are seriously considering only offering the MPX4250 map sensor (250 
KPa), not the MPX4115 (115 KPa). As I have indicated numerous times, the MS 
box will not know the difference in resolution, because MS only 
determines/needs MAP to 1 KPa, and the ADCs are only 8-bits - do the math. 
The reason for doing this is to keep Al from jumping off a bridge when he 
has to pack the kits. Having only one MAP sensor type means that the kits 
are all the same, so he can box up packages ahead of time and then figure 
out who to ship to. This allows us to get the kit to you faster as well.

We must keep Al happy and sane.

3) We will be offering PCBs separately - so you can order as many PCBs as 
you like. Depending on GB total quantity, these should be quite reasonable 
in price. I will be boxing these up independently from Al's kit activity, 
so these will be shipped separately, but one can pack many PCBs in a 
Priority Mail envelope.

4) We are going to have the processors pre-programmed by a programming 
service. This only adds a small amount to the kit price and keeps me from 
burning 500+ processors with code. Turn-around time for the service is 
about 2 - 4 weeks, which correlates with the PCB fabrication time.

5) I am working w/ Jeff on the stimulator GB - he will be posting info on this.

6) A "guesstimate" on kit cost - the MS kit in the $105 to $110 range, and 
the PCB around the $10.00 - $12.00 range. The final cost depends on the 
number of GB participants.

- Bruce


- Bruce

---------------------------------------------
              Bruce A. Bowling
          bbowling at earthlink.net
    http://home.earthlink.net/~bbowling
---------------------------------------------


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