I am working on a morse code keyboard which will connect to a transmitter.
I did a similar project on an Arduino and it took me weeks of spare moments to get it done. I had to write a program on a PC to act as the keyboard.
While I had more functionality on the Arduino version (so far) I estimate it took me about one tenth of the time to get it done with a FEZ. Hooking a keyboard to the FEZ took minutes. An interesting part was the development of a methodology to do user command inputs with morse code responses. No lcd for this project.
Of course knowing .NET, C# and having threads available did have something to do with it. Oh, I have about 20 years experience with c/c++ so language was not a big issue.
I am now thinking about how to do the actual connection to the transmitter.
It appears that the input to the transmitter is TTL like. On open key there is +5V present. To key the transmitter, and send, the input has to be grounded. When grounded, about 90 micro-amps of current are flowing. The input must be taken to less than .35V.
If I was using TTL logic I would use an open collector output to ground the input.
I could use a 2n2222 transistor and a resistor to ground the input driven by a digital output.
I thought about the relay component, which would the easiest/cleanest, but I don’t know if it can be toggled fast enough and whether it is rugged enough to take abuse of a keying relay. The fastest I would use it would be at 40ms and 120ms pulses, which is 30 words per minute.
I noticed that some of the Domino pins are open drain. I think these might be equivalent to open collector? Can I use one to ground the Tx input?
Anyone have a suggestion on the best/easy way to proceed?