We are trying to capture data from a custom PLC (a Richard Simon Computapak II controller) controlling a Richard Simon 25kg sack filling machine.
The output from the PLC appears to be 5mA-20mA common loop and currently outputs to an Epson LX-400 printer, which has been replaced several times and is now failing again (a similar machine has now been operating for 6 months without a working printer).
The current loop connection to the Epson 8143 serial card is peculiar in that there is just a single RxD wire to pin 25 on the DB25 at the printer end plus ground (and a 47 ohm resistor connected between pins 23 and 25).
We want to extend the working life of the equipment by converting the current loop signal to RS232 and capture that with a 12v RS232 to USB adaptor plugged into the Raspberry Pi. However, the only convertors we have found (and tried) do not work without both an RxD+ and RxD-. One company suggested that this was analogue current loop but we cannot find any details. We have been unable to spot any useful output marking on the circuit board for the controller.
We have even tried using the existing Epson serial card with an external power supply to read the RS232 data coming off that serial card which does at least allow us to capture data, but the RS232 output is gibberish.
Epson have not been at all helpful - as the UK branch say that the printer was only sold in New Zealand (even though the printer is stamped Epson Telfod (UK) Limited, so we have to contact them, and Epson Australia tell us to contact Epson UK. The UK branch then told us to contact the original supplier (who went out of business many years ago)
For example, we capture an "a" character but it appears on the printed page as "=".
We thought maybe we just need a lookup table to translate the characters to the correct ones, but then you get character 134, which can either be a space or colon on the printed page for example!
We have managed to find a badly scanned Epson 8143 manual, plus a later 8148 manual which shows the schematic (attached), which looks correct. We must be missing something.
The schematic shows the Current Loop TTY RxD connected to pin 25 (on the left).
There is then a 47 Ohm resistor connected to pin 23 (TTY RxDR)
All of the jumpers are set to allow the signal to come out on Pin 11 (on CN2 - right hand side). - this should be RS232 according to the other documes we found and replaces the simpler RS232 RxD signal on Pin 3 of the DB25 serial connector.
Ground (Pin 7) and Frame Ground (Pin 1) are connected.
We have a traco and extrenal power supply supplying 12v on Pin 20 (of the CN2 connector).
The RS232 CTS is then used to provice 5v on Pin 16, with ground from the power supply and RS232 connected to pins 24 and 25.
Open to ideas on what we are missing!
The output from the PLC appears to be 5mA-20mA common loop and currently outputs to an Epson LX-400 printer, which has been replaced several times and is now failing again (a similar machine has now been operating for 6 months without a working printer).
The current loop connection to the Epson 8143 serial card is peculiar in that there is just a single RxD wire to pin 25 on the DB25 at the printer end plus ground (and a 47 ohm resistor connected between pins 23 and 25).
We want to extend the working life of the equipment by converting the current loop signal to RS232 and capture that with a 12v RS232 to USB adaptor plugged into the Raspberry Pi. However, the only convertors we have found (and tried) do not work without both an RxD+ and RxD-. One company suggested that this was analogue current loop but we cannot find any details. We have been unable to spot any useful output marking on the circuit board for the controller.
We have even tried using the existing Epson serial card with an external power supply to read the RS232 data coming off that serial card which does at least allow us to capture data, but the RS232 output is gibberish.
Epson have not been at all helpful - as the UK branch say that the printer was only sold in New Zealand (even though the printer is stamped Epson Telfod (UK) Limited, so we have to contact them, and Epson Australia tell us to contact Epson UK. The UK branch then told us to contact the original supplier (who went out of business many years ago)
For example, we capture an "a" character but it appears on the printed page as "=".
We thought maybe we just need a lookup table to translate the characters to the correct ones, but then you get character 134, which can either be a space or colon on the printed page for example!
We have managed to find a badly scanned Epson 8143 manual, plus a later 8148 manual which shows the schematic (attached), which looks correct. We must be missing something.
The schematic shows the Current Loop TTY RxD connected to pin 25 (on the left).
There is then a 47 Ohm resistor connected to pin 23 (TTY RxDR)
All of the jumpers are set to allow the signal to come out on Pin 11 (on CN2 - right hand side). - this should be RS232 according to the other documes we found and replaces the simpler RS232 RxD signal on Pin 3 of the DB25 serial connector.
Ground (Pin 7) and Frame Ground (Pin 1) are connected.
We have a traco and extrenal power supply supplying 12v on Pin 20 (of the CN2 connector).
The RS232 CTS is then used to provice 5v on Pin 16, with ground from the power supply and RS232 connected to pins 24 and 25.
Open to ideas on what we are missing!
Statistics: Posted by RWAP — Tue Jul 29, 2025 1:57 pm