[GreenKeys] Current Loop Question

[Mike Douglas]

Considering a 32/33 with a UCC-6 connected across the room to a computer:

The receive side (data to the printer) clamps the positive side of the loop to less than 0.8v or so above the negative side of the loop. The sender can get by with a very low loop voltage as long as it can source the required 20ma.

On the transmit side (data out of the teletype), the voltage has to be high enough that the fairly high resistance of the carbon distributor wiper plus the contact resistance of the keyboard, reader, or answerback is not a factor in the receiver’s sense circuit. I’ve never had a problem using 12v for this loop.

Mike

> On Sep 27, 2020, at 6:01 PM, GodOfCows <jacobdouglastupper at gmail.com> wrote:
> 
> I understand the Teletype 32 uses a 20 mA current loop, does anyone know the voltage of this loop?
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