[GreenKeys] Current loop not providing (enough) current

[Zach Zarzycki]

oops sent same images 2x

these are the correct images.

I'm hooking my loop up as the R and T to 1 and 2 - into the where would be
the termination of 4 and 5 on the one image - to the teletype at 15 and 26.
All the jumpers are set the same way as the 2nd image (11-12-13) and (14-15)

https://imgur.com/YQPuMJ7
https://imgur.com/FQKJe3C

On Mon, Sep 23, 2019 at 10:24 PM Zach Zarzycki <shardsofaperture at gmail.com>
wrote:

> Here is the 2 points I'm hooking up at - would be pins 15 and 26 (also my
> test points that show the 48 ohm)
> https://imgur.com/a/TGrywcg
> https://imgur.com/FQKJe3C
>
>
> On Mon, Sep 23, 2019 at 7:55 PM Zach Zarzycki <shardsofaperture at gmail.com>
> wrote:
>
>> I'm thinking I need to boost the voltage overall. The darn loop only
>> shows 48 ohms which feels wrong when I grab each end of the loop with the
>> meter. The schematics are cryptic as all get out but I'm positive on this,
>> where it shows the plug for the table, is where I need to wire my loop in.
>>
>> I'll have to snap a photo of the schematic I'm looking at, but seeing as
>> how they keyboard works to TX to the computer terminal, I'm pretty sure I'm
>> where I should be.
>>
>> I went on mouser today and bought the linear 120vdc supply so when that
>> comes in I'll try hooking that up though a 2k and see if it makes a
>> difference.
>>
>> I will say there are 2 5k resistors on the unit in different places, but
>> they're not in the loop so to speak, especially as seeing I only read the
>> 48 at the +/- twx line connection (where I hook my loop power supply and
>> board into).
>>
>>
>> *From:* js at teletype.net
>> *Sent:* 22 September 2019 12:26
>> *To:* greenkeys at mailman.qth.net
>> *Subject:* Re: [GreenKeys] Current loop not providing (enough) current
>>
>> I'm certain that's the problem. I've done some testing on my Models 15
>> and 19 in the past, and if the 26 magnets are in the same realm of
>> tolerances, they'll start to become useless at around 50mA, give or take.
>> 25mA is much too low a current to have any effect.
>>
>> The keyboard is keying the loop successfully since that's just
>> mechanical, and the board can pick up signals even lower than 20mA, but the
>> selector magnets can't.
>>
>> The question is why. Looks like you expected 96 volts and so calculated
>> 1600 ohms resistance to get 60mA. However, it sounds like there's more
>> resistance in your loop. A few hundred ohms is expected, but you've got an
>> additional 2.2k ohm and change.
>>
>> I'm willing to bet the loop may already have a 2k ohm resistor in series
>> somewhere-- maybe installed within the machine itself if you have nothing
>> else on the loop. Try measuring resistance in the full loop with and
>> without your extra resistors, and I'd guess you'll see the same thing. As
>> long as you see roughly 2000 ohms on the loop without your extra resistors,
>> it will be safe to power it without the extra resistors. At 96 volts,
>> however, you'll get a current of only around 40 - 45mA, which probably
>> won't reliably trigger the magnets. But who knows, maybe it'll work fine--
>> it's always worth trying.
>>
>> If not, you'll either need to locate and replace that 2k resistor with
>> your 1600, or you'll need to boost the voltage.
>>
>> -
>> Jordan Spencer Cunningham
>> teletype.net
>>
>>
>> On Sat, Sep 21, 2019, at 9:37 AM, Zach Zarzycki wrote:
>>
>> Well - I have my 26 hooked up though the volpe board and have managed to
>> get as far as when I type on the teletype's keys the terminal window on the
>> laptop accurately displays what I've punched up.
>>
>> However, typing on the teletype doesn't cause the keys to punch paper,
>> and typing on the laptop keyboard won't cause the teletype to do anything.
>>
>> I'm set up with a boost converter and a 12v 3amp power supply that SHOULD
>> be supplying roughly 60mA at 97 volts though the loop after being boosted
>> and then ran though about 1.6k wire wound resistor (600 ohm and a 1kohm in
>> series, both 25W rated).
>>
>> The problem is when I read the voltage out of the booster, it shows  97v,
>> but the most I've seen any amperage on any test point is 25ma, a far cry
>> from 60ma. I'm wondering this this is possibly the reason for the computer
>> keyboard not being able cause the keyboard close the magnet and select a
>> letter then type.
>>
>>
>> My gut says maybe? But I find it very odd though that I can make the
>> greenkeys act as a keyboard, so maybe I'm missing something else.
>>
>> Zach
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