Good news & bad news

With thanks to a commenter on a previous article, I’ve had a close look at the ribbon cable which connects the TC35 module to the UART board. After a bit of fiddling with the (tiny) clamps which hold the cables in I was able to release the cable. At least one of the contacts appeared damaged, so I trimmed the end off each cable with a sharp pair of scissors and reconnected it. This picture shows the two boards disconnected with the ribbon cable in the middle. Normally the two boards are on top of each other and I imagine that the ribbon is under a bit of strain.



Initially there was no change – but then I tried reversing the TX & RX pins (ie connected TXD – TXD rather than TXD – RXD) and all of a sudden- success! I can now control the module through AT commands using my new USB device.


So thinking I had solved the problem, I rewired the cable to the alarm panel (swapping TXD & RXD) and tried it – but once again with no success. I’m not quite sure what I’m doing wrong, or I suppose it might be that there is some other reason (maybe incompatible voltages) why this unit doesn’t work. I did wonder if it was because my SIM has no credit but it should still report signal strength and it does so if I try sending AT+CSQ directly.

So if anyone else out there is struggling with one of these modules – try trimming the ribbon cable and swapping over the TXD & RXD pins.

Meanwhile I have received the new board from China – which is tiny by comparison with the one I have. I know from Andy that this definitely does work, so I’m now waiting for the regulator board to arrive and I’ll give it a go.

6 thoughts on “Good news & bad news”

  1. Hi,

    Could it be related to the 2 stop bits?
    For the IP modules a double stop bit is needed as mentioned in your previous blog (19200 baud, 8 data bits, no parity, 2 stop bits)
    I used a Sollae EZL70 as IP module and is working just fine.

    I’m also looking to fit a GSM module.
    I still have a GM28 module and was thinking of fitting this.
    Not sure however if it 2 stop bit capable.


  2. Yes, that’s a good point. It probably is that. However it clearly isn’t a problem for all gsm modules luckily, si maybe just a case of trial and error

  3. Did you need to configure something for the SIM800 module? (init string or just plug and play?)
    Thank you

  4. i am successfully using a mc35 terminal module. I really didnt look into the communication on signal level but only on at command level and it worked directly.. as far as i can remember the mc35 supports auto baut rate detection.. so maybe this option did the trick

  5. Yes, I think that the problems I had were related in some way to the baud rate. It is rather hit and miss what you get from the Chinese sellers on ebay!

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