Railway modem module made by Polish company ISM 868 MHz RM-2 - interior and construction

Another interesting piece of equipment from the liquidation - an 868 MHz ISM modem. This time it's also badly battered, but maybe it's worth looking inside anyway? Already from the casing it is interesting - I don't see a power connector, there is only an Ethernet socket. Could we have POE here, or maybe someone just used the connector in their own way?

Other than that, we only have a BNC antenna connector:

We take a look inside.

There are two boards inside - the motherboard and separately the RF module. The main board has a clearly visible separate power supply section and a separate digital section with display, switches and RS232 connection for the service technician.

On the input we have status LEDs, and just behind them you can see the PTC protection thermistors. With the RJ45 connector actually goes the power and communication, a little further on we have a dual power section with voltage reduction inverters.

This section is based on two LM2575S, one probably generating a voltage of 5 V and the other 3.3 V or similar.

Right next to it are two SP485Es - these are RS-485 half-duplex transceivers. This explains what standard the communication is in. It is not Ethernet, however.

The main microcontroller is a 32-bit H8/3052 made by Renesas with 512 KB ROM and 8 KM RAM. Next to it I see a BS62LV1027 128 KB memory. Nearby is the SP706SE, which is a supervisory circuit (watchdog and voltage monitor).

Further on we have an RS232 service connector along with a TTL to RS232 converter (ST232C), DIP switches and a 7-segment service display. the 74HC14D is a Schmitt flip-flop (buffer) and the HC00G is a NAND gate circuit.

Under the RF module is there room for some more circuitry - memory? Or is it for a module in surface mount format?

Bottom of PCB:

Here, as standard with this type of module, two 24C04WP EEPROM memory bones:

Plus a 74HC165D sliding register - perhaps to control this display?

For the RF module itself, I don't know what I can write, there are no markings on the circuitry, is anyone able to identify it?



I have connected the power supply. The red LED lights up for a moment. The display quickly counts down from 1 to 9, ending with zero again. The green LED stays lit.


Basically that's it. I have no documentation for this device. Potentially a USB to UART or RS485 converter could be attempted, but without knowledge of the protocol I would be unlikely to expect much. Have you encountered any modules of this type? Feel free to comment.

PS: How do I know "railroaded"? Unconfirmed information from parts donor.