As you might have noticed, sometimes I work as freelancer in electronics =) It applies not only to fixing PC electronics and mobile phones, but also to repairing, modifying and designing my own solutions in consumer electronics. One of the projects I worked on yesterday is modifying MSR-206 magnetic card reader to replace RS232 port with USB. Let me tell you about that…
This was of high urgency, so I’ve had to suspend my usual work activities and concentrate on this project yesterday. MSR-206 is a pretty impressive piece of technology, incomparable to those cheap eBay magnetic card readers. It even includes 24V 2.2A DC power supply, which is quite heavy and makes you question those cheap USB 2.5W card readers – like, are they really OK for most applications when somebody released such a powerful thing just to accomplish the same task? It’s also kind of state-of-art inside… Well, maybe it’s just me being used to see a lot of disassembled Chinese stuff =)
Unfortunately, it also is quite old – it has only RS232 port in 8P8C (Ethernet cable) form-factor, not to mention non-standard wiring. My acquaintance working as the IT guy in one hotel had to replace the receptionist PC with a newer one. He didn’t think of need of having a COM port, though. Also, the original COM-8P8C cable was lost, and, of course, cheap COM-8P8C cable for connecting to network equipment didn’t work. So – there’s a hotel that needs their equipment to be in working state ASAP…Which meant replacing RS232 with USB. RS232… I instantly sensed MAX232 chip inside.
On the left side, you can see something related to a power supply. Logic runs on 5V anyway – so I’m not supposed to look closer and examine =)
L293D? OK, maybe there is a motor or some kind of motor-like thing inside =) Wasn’t exactly my job to figure it out.. 3 of them is something, though. I also didn’t want to see what’s the chip with a sticker on top – must be a MCU, and I knew it didn’t matter to me because I wouldn’t understand it anyway =) Those old MCUs are a PITA when you have to somehow change contents of the ROM or something like that.
Some kind of logic elements… OK, that’s not what I’m searching for. Let’s see the bottom side of PCB.
Some more logic elements, I guess I’ll have to examine them in case somebody got high and implemented UART-RS232 using buffered logic gates.
Woohoo! The object of my search. As you know, MAX232 has 2 RS232->TTL (R-T) elements and 2 TTL->RS232 (T-R) elements inside. One pair of R-T&T-R is RX and TX. Other pair is usually unused… Usually. Let’s desolder the chip to see what’s actually used…
For more detail: Remaking MSR206 RS232 magnetic card reader to USB