Hi all,
After a bit of help/confirmation, my sister has some vending machines, she's just bought another second hand and wants to add a card reader to it and use the same make as the other so they can operate on the same account.

Vending machine is from one seller, card reader from another.

Should be fairly simple plug and play.....
She asked me to have a look as there was an adapter cable supplied with the vending machine. I put my multimeter on in to check pinout was right and the supply is 32v DC.

The card reader has 12-24v DC written on it.
A call to the manufacturer of the card reader and they said they wouldn't warrant it at 32 volts.

I've had a look at the vending machine power supply, it has 24v ac transformers which after rectification gives as would expect 32v .

Is this a standard in the vending machine industry? The card reader talks to the machine via a multi drop bus which seems fairly standard, this specifies 24v supply. Rs232

I was thinking of making a simple 24v regulator to supply the card reader.

If I do this might I run into problems with signal levels on the rs232 with the rest of the system running at 32v?

I've a feeling the card reader 'might' be ok at 32v but seems cheap insurance to use a couple quids worth of components to be sure?

Sorry for the long winded post!

Cheers Geoff

 

RS232 operates on +3V to +15V so the unit must include some voltage source providing the required voltages. See this wiki article on the subject:-


https://en.wikipedia.org/wiki/RS-232

 

24 VAC is rms (root mean square).
Peak voltage is rms x 1.4
When AC is rectified to DC, the reservoir capacitors will store peak DC voltage.
32 VDC sounds about correct after subtracting 1.4 V for loss across two rectifier diodes.

You can use a 24 V voltage regulator to reduce the voltage to 24 VDC.

 

Thanks, I made up a little online regulator with a lm317 I had lying around, then suspicion got the better of me and I searched for a datasheet for the card terminal, which I found quite easily!

Maximum voltage on the multi drop bus power input, 34 volts. So either the person we spoke to didn't know what they were talking about or couldn't be bothered to check their own datasheet, or both of the above?

Thanks for taking the time to reply, I'm slightly wiser that I was......