22 Sep
2013
22 Sep
'13
12:13 p.m.
It looks like the receive-loop current from the W076
will be around
43 mA (a current meter between pins 3-4 for example) which seems odd,
but that's what my calcs say, unless I've misinterpreted something in
the schematic. But it matches what you've been seeing doesn't it?
Originaly, it was probably designed to connect to a Teletype Model 33
raehr than 'any old current loop device;. Said Teletype was designed to
be used in 20mA or 60mA loops, there's a jumper wire to shift to set the
receiver current threshold. But the transmitter is just contacts. It
doesn't care waht the current is, within reason. If it works at 20mA
nand 50mA, it'll work at 43mA or whatever too.
My guess is htat DEC designed this thing to sue the supply rails that
were available and stnadard components. And that's all.
-tony