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

[Duncan M. Brown]

John,.

Thanks for posting your circuit.

Any special reason why you put the two sections of the HRS312L in
parallel??  In series connection, it can handle 190 ma and will not be
polarity sensitive.  (Wouldn't matter if you always have the same loop
supply connected through the same cable; I'm just thinking about more
general usage.)

  Duncan, K2OEQ


> [Original Message]
> From: John Nagle <nagle at animats.com>
> To: <greenkeys at mailman.qth.net>
> Date: 14-Feb-09 00:03:01
> 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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