Digital LC-1 problem

[Marek]

I have twin Lc-1s connected with a terminator plug at one end and a serial cable connecting the tip to pin2, ring to pin3 and screen to pin5. The cable goes to a rs232-ttl module purchased on the net and this is connected to an IOExtender. This has 5v connected to the 5v at the proto area; ground connected at the ground connection at the 12v/ground pair of connections close to the 12v/ground pairing at the power supply input and F0 connected to TX and F1 connected to RX on the rs232-ttl board.

The IOX board shares its 12v with MS3 and its ground with the MS3X connector. The LC-1s have their sensor grounds at MS3 and MS3X and their heater grounfds to the block.

In short, all of the wiring is as per the manual, although I note that there is scope for earth loops in the approved documented arrangement.

The rs232-ttl module has a pair of leds on it. When powered up, the RX led flashes constantly and quickly, but the tx led is continuously bright. The F0-TX connection reads zero volts and the corresponding rs232 connection reads at the tip of the LC-1 line reads 8.6v.

Worryingly, although the RX led flashes, F1 reads 0.3v, which is too close to zero for my liking, but this may simply be a reflection of 0v/5v average conversion coming from the LC-1 chain.

This suggests to me that the rs232-ttl module works as it passes logic low 0v TX from F0 to make 8.6v on the RS232.

The IOX is connected via CAN and this appears to work fine. When MS3 is configured to look for CAN EGO at offset 153, it records the error condition afr as set in the software, less 0.1 AFR which I am guessing is down to rounding.

Other parts of the IOX setup look to be working fine over the CAN. MS3 is configured with the defaults for IOX.

The first time the unit was powwered on, it found the correct CAN EGOs and displayed the AFRs as normal (22.3 once the LC-1 programmed defaults had disappeared on booting up the LC-1sa) - i.e. it was working correctly. On turning the key to start the engine, the LC-1s dropped out and when they resumed, both LC-1s were reading 15.6 and it has been ever thus.

This has happened with more than one max232 chip and with the purchased module. One of them was a MAX232CPE and another a MAX3232, i.e. it hasn't been exclusively 3.3 to 5v chips for the ttl-rs232 converter.

The LC-1 chain when plugged into logworks instead of the IOX reads both channels normally.

Can anyone shed any light on what is happening please?

kind regards
Marek

[racingmini_mtl]

The best thing would be if you can scope the signal on both sides of the rs232-ttl converter. If you don't have an oscilloscope, you could use a sound card scope as shown here: http://www.msextra.com/forums/viewtopic ... 32&t=38560. Since the LC-1 signal is at 19200 baud, you should be able to see it even on that low frequency scope.

Also, can you post a picture of where you have connected everything. I'm not clear on how you have everything setup. I'm also not sure why you talk about 3.3V since that should be running at 5V.

Jean

[Marek]

Thank you Jean.

The IOX firmware baud rate for the second serial port (GPS/LC-1) was set at its default of 9600 baud. Changing it to 19200 makes all the difference and the display now picks up the AFR of 22.3 as soon as the LC-1s have booted up, rather than staying at the broadcast default error AFR setting.

(The reference to 3.3v was relevant only in that the max3232 is the lower voltage version of the max232 chip, so any potential voltage above 5.5v may more probably damage the max3232 chip over the max232. The chip does indeed run at 5v, from the 5v line.)

kind regards
Marek

[racingmini_mtl]

The default baud rate is correct for the GPS module but unfortunately it's wrong for the LC-1. I should add this information on the screen besides the settings so that it is more obvious for anyone using it.

Jean