[GreenKeys] MMTTY & Mercury Relays

[Tom Hunter]

Steve Bennett,

My "FOX" generator is MMTTY. I copied the opto isolator
driver from the ubiquitous Easy Digi Interface board.

http://www.davegardner.org/Ham/PDF/SoundCardKit.pdf

(If you are transmitting RTTY from a computer, that board is the easiest way to keep RF away fom your computer. I highly recommend it.) I buy two at time, with shipping they run about $9 each. Search eBay for the best price.

My opto isolator drives a mercury wetted relay which in turn keys my local loop. Those relays are plenty fast enough.  Be sure to use spark suppression across the loop contacts of the relay.  .1 mfd in series with around 330 Ohms  1/2 watt should do it. The relay can key a 20 or a 60 mil loop.

My relay needed 12 VDC, I used a wall wart to power it. Power yours according to your relay but observe the maximum voltage of the opto.

The sense is reversed. You must use Normally Closed contacts on the relay.

Hint: do not wire both RTS and DTR thinking you can use either. Neither  will work. Wire one or the other. (Learned from hard experience.)

It is a little tricky to use the FSK output of MMTTY.
In Options, go to the TX window and set the Port for EXTFSK or EXTFSK64. At that point I think you will have a window to select RTS or DTR. I stick with RTS to be consistant.

The scematic above will show how the wire th DB-9.

In the DECODE window set the baud rate, bits and stop bits.

Go to the MISC window to select FSK.
I like SOUND + TxD  (FSK)  Then I can use the AFSK output to test a Terminal Unit or to set the tones on a Dovetron

 Test it. If it keys your loop sucesssfully, go back to the TX window.

 I also like to check "Double Shift" I find Unshift-on-Space a Nuisance, so I uncheck it. Now grab an unused macro button, name it FOX and type in your FOX. I like to start all my macros with "%L%L" (two LTRS characters) If you end your text with a pound sign, it will type forever ( Like their RY's) unless you hit the TXOFF button.

Look at their RY text to see how they do it.

Now you have a FOX generator and an RY generator
plus whatever else you may want to type in.

It is a darn shame that whatever MMTTY receives does not come out of the FSK, otherwise you would not need a hardware TU to receive off the air to to your Teletype. 

You need to find a relay that will operate positively on the optoisolator.

Jim Cooper says he has a cellar full of mercury  relays.

I just asked him to let me know if he has a suitaable one. When he answers I will pass it on to you.

It takes a relay that will close positively on 12 to 24 volts DC.  of course you must supply that voltage. A mercury relay is polarity sensitive. Coils are usually on pins 7 & 8. Pin 8 is positive.

A mercury relay must be nearly right side up or the mercury will short all the contacts together!


Tom  N3CRK