How do you get the UPI to work with 2-wire pagers?

[Zack08]

Last week I built the myself a copy of the UPI. It seems to work okay on the 3-wire Advisors(even though it kicks me to the password screen ). Anyway, I cant figure out how to tie the Tx and Rx lines together to interface with the Advisor Gold and other 2-wire pagers. I found a site where somebody mentioned tying the two together with a 3K resistor, and then connecting the Rx wire to the pager. I cant get this to work, nor can I find a resistor value that will. Does anybody know how the Tx and Rx lines are connected together in an authentic Motorola cradle?

After trying for a week with no success, any help is GREATLY appreciated.

[aaknitt]

No guarantees that this will work, but you could try a 10k resistor from UPI RJ11 connector pin 4 to pin 2 and a 1N4148 diode from pin 2 to pin 1 (stripe towards pin 1). That's just a SWAG...let me know if it works. Have you tried just shorting them together without anything in between them? That works on some interfaces.

Andy

[Zack08]

I tried both of your suggestions and it still says "Pager is not responding."

I've completely run out of ideas. The only real difference between my UPI and the Motorola one is that I'm taking the Tx line straight from the MAX232 instead of taking it from the output of the LM339. For some reason, I just cant get that portion of the 339 to work, but since it looks as though it is functioning as a non-inverting comparator, taking the output straight from the 232 should be electronically similar (please correct me if I'm wrong ). The line which takes data from the pager, however, is fed into the 339 as normal.

I dont know if there is a problem with the LM339 portion that I am missing, or if we still haven't figured out how these two lines are properly connected.

[aaknitt]

Yeah taking it straight out of the MAX232 shouldn't be a problem. I was basing my suggestions off of this schematic for a 2-wire programmer for the Radius series of radios (which is known to work on the radios):

http://www.batlabs.com/images/mrib.gif

I was hoping that it would be the same for the 2-wire pagers. Other variations of that same schematic are on the RIB-building page on Batlabs. Most of them use two sections of a 7407 inverter to buffer the TX and RX of the MAX232 together, so something along those lines may work.

Andy

[Stmills]

I have used a programmer i made for Kenwood radios to program both 2 and 3 pin pagers. My 3 pins are Ground, DFR and DTR, I read somewhere online to place a 1k jumper from DFR to DTR as 1 pin and ground as the other. I have used this for an Advisor, Adivsor Gold, Advisor Elite.

[515]

If it helps anyone, I just programmed an Advisor Elite without the cradle. I used the real UPI, though. I made the UPI-to-pager cable by soldering a couple of pins to an old 4-wire phone cord. I just tied the TX & RX data lines together (with no resistor) and soldered one pin to those, and soldered the second pin to the ground wire. The 1.5 V line wasn't used, as I kept the AA battery in the pager during programming.

The ground wire goes in the hole closest to the battery on the Advisor Elite. The LED on the UPI should light once both pins are inserted in the pager.