[GreenKeys] Interface board for Model 15, schematic and parts list (RO version)

[Lester Veenstra]

Very nice
Will be watching for follow ons
In the 12/14/15 and high level 28 keyboard context, conventional wisdom was
the HV/60 ma loop was beneficial to keep oily contacts clean.

How about an RS-232 interface powered opto isolated ciruit to go from 60 ma
loop back to rs-232 for input to PC?
 
Lester B Veenstra  MØYCM K1YCM
lester at veenstras.com
m0ycm at veenstras.com
k1ycm at veenstras.com
 
 
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-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of John Nagle
Sent: Saturday, February 14, 2009 5:35 AM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] Interface board for Model 15,schematic and parts list
(RO version)

    For those of you who've been asking, here's the circuit I'm using
to drive a Model 15 with a 60mA current loop.

http://www.animats.com/nagle/images/teletype/converterv2outputonly.png

Parts list (with Digi-Key part numbers):

C1	100pf	1457PH-ND
D1		MBR1100RLGOSCT-ND
F1		F1471-ND
IC1	HSR312L	HSR312L-ND
J1		WM4204
J2		A32075-ND
J3		WM4200-ND
R1	100	100QBK-ND
R5	1K	1.0KQBK-ND
R7	2K 10W	TA810PW2K00JE-ND
R8	68K 1/2W	68KH-ND

This has been banging out copy for a few hours now.

It's intended to drive one 55 ohm magnet from a 120VDC supply.
Measured loop current through a Model 15 is 59.9 mA.

I'm working on the keyboard interface, but for those of you who are
blowing out parts trying to switch a 60mA 120V current loop, here's
something that works.

The HSR312L optoisolator is good for 300V, and there's a little bit of
snubbing
(about 1us of decay time) to keep the worst-case inductive kick down.

The thick-film 2K 10W resistor is a nice way to dump 10W; it's PC mount with
four pins, and has a high surface-to-volume ratio, so it doesn't get as hot
as rectangular ceramics, and can be board-mounted.

					John Nagle
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