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HOWTO: PoS Printers powering a mAP Lite

Wed Sep 16, 2020 5:00 am

Many ethernet based point of sale printers have an RJ12 connector that has 24V supply on it for a solenoid activated cash drawer. If you have such a printer without the drawer being used you can power a mAP Lite (or many other Mikrotik devices) from it to give the printer inexpensive Wifi client capabilities. I have done this with Epson thermal PoS printers out at the bar and kitchen to make them wireless and you don't need to fuss about with a USB cable and a 5V supply which isn't always easily available or convenient.

You will need:
* A short length of Cat5 cable (for the thin copper wire).
* RJ12 crimp plug connector
* 2 x RJ45 crimp plug connectors
* RJ Crimping tool.
* Some experience crimping RJ45 cables and some nous to work things out for yourself.

Check the pinout of your printer drawer socket for the power pins for example:


On the RJ12 I used pin 1 for ground and pin 4 for the 24V supply.

This is the Mikrotik reference for PoE on the RJ45 and also Wikipedias PoE pinout info.
* ... utpolarity
* ... et#Pinouts

On the RJ45 I used pin 4 for positive rail and pin 8 for ground.

Connect both RJ45's plugs pins 1, 2, 3 and 5 for 100Mbit data. You'll have to do it in such a way so that there is enough length of blue (pin 4) and brown (pin 8) wire on one end of the Cat5 so that it'll reach the RJ12 socket when the RJ12 and RJ45 are connected into the printer. Crimp the RJ12 with the power wires in the correct position. Meter out and test and verify the cabling before you plug in the mAP lite. I won't be responsible if you destroy any hardware with incorrect wiring.

If you use a short run of Cat5 you can use double sided tape to attach the mAP lite to the back of the printer.

* I did find that in pseudo-bridge and pseudo-bridge-clone mode the DHCP request from the printer wouldn't work to the ISP Wifi router. I had to make the printer IP static (a static IP is probably wise anyway as the Kounta restaurant app wanted static IPs for the printers.)
* I ended up putting in a Mikrotik WAP (hAP Mini) just for the PoS devices and put the mAP lites in station-bridge mode. Mikrotik->Mikrotik always works better in these cases.
* I have not tried this setup in parallel with a cash draw, but I assume if the solenoid is activated the 24V rail will drop too low for a brief period and reset the mAP lite.

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