2 group DIY transmit modem

[number 7]

I can't seem to get anyone from MoTeC UK support to help me on this, so I thought I might have better luck here:

I'm having someone make a transmit modem / computer interface (clock generator) based on the MoTeC circuit posted on another thread here recently. I've no idea about the technical side of this, but the questions are really do you need a power supply for this unit, or does it pick up from the ecu somehow?

And :" Okay, I've designed the board assuming there's no PSU required; it's quite small (about 60x40mm) - however, I have come to the conclusion that the 74HC151 isn't really needed.

When I'd initially looked at the schematic (thanks for the higher resolution version - there were some numbers I wasn't 100% sure of, although I'd guessed correctly), I thought that it was able to select one of two frequencies, either generated by the inputs I0 or I3 depending on whether pin 1 is high or low.

I'd missed the fact that pin 1 is actually the power, so it's always high.

This means that I3 is always selected, and this is just selecting a 153.6KHz clock to output on pin 8.

This means that pin 8 could be generated by the 74HC4060 directly from the Q5 clock.

Or, it could be DRASTICALLY simplified by using a programmable divider - and one happens to exist at the right frequency.

Could you check with MoTeC if it's just a conditioned 153.6KHz signal that's required on pin 8, please? If so, then the design can be simplified and it would be easier to wire up. (The signal conditioning is done with R3 and C5, which I believe I'd need to replicate).

Thanks

[CamB]

To celebrate these ECUs being >25 years old, I thought I'd have a go at the circuit referred to above, and in the link below:

download/file.php?id=96

It seems to me that the 74HC151 is redundant to the circuit as well. What I would assume (apologies if this has wrong terminology - am new to this) is that:

- the crystal generates a 4.9152Mhz signal
- the 74HC4060 divides it, to what depending on the pinout
- pin Q5 has divided to 153.6Mhz (which, divided by 16, is 9600 baud)
- pin Q6 - Q8 are half each time, equating to 4800, 2400 and 1200 baud - all options for the PC software
- the hard wired configuration of the selector pins A-C on the 74HC151 mean Q5 is only ever passed through
- once upon a time the original circuit probably had dip switches (or something electronic) to allow configuration for 4800, 2400, 1200 baud
- but as these aren't necessary - I should use 9600?

IF anyone reads this ... thoughts? Any value in implementing the ability to switch to a lower baud rate (would it help likelihood of successful comms)?

[SprinterTRD]

Yes the HC151 can be omitted.
Just use the output from the 4060 to drive the 2 group at the baud rate you want to use.

[CamB]

Awesome - thanks. Will give it a go - probably with a toggle switch for 9600 vs 4800 baud, just in case.

[CamB]

I thought I'd post where I got to with this, as I assume every couple of years someone comes looking for the info.

I have a working DIY transmit modem etc, and have successfully got into the ECU. Ignoring a switch I used that isn't really relevant to what's needed to work I did the following:

- followed the supplied diagram above, however I am only using Q5 on the 74HC4060* and ommitted the 74HC151
- I needed a lower ohm resistor for R2. My crystal (no datasheet - not ideal*) wasn't oscillating, so I tried it with no resistor (just wire) and it worked, so I used what I had handy - a 470R. 470R might be a bit low, but I have spare crystals etc
- the circuit is powered by the ecu's +5v (pin 1 on ecu)
- I took the Motec TX (pin 5) and RX (pin 9) and fed them into a MAX202, which outputs serial to pins 2 and 3 on a DB9F serial plug. This plugs directly into the PC (ie, no need for the Motec PCI cable)


If anyone else in New Zealand has one of these ecus and needs to borrow the converter (or wants some parts to make one), happy to oblige.

* being in NZ, sometimes you take what you get. In my case, I ordered the correct 74HC4060 and crystal from Digikey, then grew impatient and used what I could find at a local electronics store which is an HFC4060 (a bit marginal with a 5Mhz frequency input, but mine seems ok) and a crystal with no datasheet, so no way of knowing what capacitors should be.

[terryo]

i still have a 2 group ECU in my old race car. it seems to work fine except for the flakey hand controller. will this "transmit modem" you describe delete the hand controller and allow comms otherwise??.

[CamB]

Theoretically yes, as long as your 2 Group is one that can communicate with an ECU (the good people of Motec might be able to tell you if they all can or not).

[SprinterTRD]

You need version 3.3 or greater to be able to use the PC software.

You will also need a laptop with windows XP or less to make it work.

[CamB]

You will also need a laptop with windows XP or less to make it work.

For completeness...

- I have used mine on an old HP laptop with a serial port, running Windows 2000 - worked fine, but no battery
- I have (and continue to) use it on a Lenovo with XP through an FTDI USB-serial adapter - works fine
- I have tried it on a new laptop with Windows 10 using DosBox. The FTDI adapter means there is a serial error in DosBox ("Serial1: Desired serial mode not supported (9600,5,n,1)") ... but having said that it seemed to talk to the ECU ok. I wasn't brave enough to keep using it

[SprinterTRD]

It can be a challenge getting 16 bit software working on 64 bit systems which is why I suggested XP.