I'm finally taking Morse Code classes, trying to learn my dits and dahs. So I naturally poked around the various Morse projects in the forums. But now I have a more nuts-and-bolts kind of question.
I purchased a nifty antique telegraph sounder (basically a relay, when the clicking and clunking represents Morse dits and dahs). There are several projects online to interface such a sounder with a *duino or a Raspberry Pi (such as http://sigalonhowtod...since=318825083). What I'm looking for is the best design that will protect both my Netduino and my antique sounder.
The sounder has a 4-ohm coil, and (according to http://www.morsetele....org/wirechief/) was designed to run off an approximately one volt 'Gravity Cell.' The same article suggests running the sounder off a D-cell battery (current draw estimated at 200 mA).
As I said, there's a lot of suggestions online for how to connect the sounder. Most use a simple transistor to switch a 5 volt power supply to energize the sounder's coil. This seems a bit high to me, but since the sounder is built like a concrete bulldozer, I could risk it.
More to the point, what kind of snubbing configuration would you recommend to protect the Netduino from induced EMF. Most folks seem to use a simple diode in parallel with the coil (which would shunt the induced current safely to ground). Some add an LC circuit; a few suggest replacing the simple snubber diode with two Zeners (diodes wired in series, cathode-to-cathode, then attached in parallel with the coil).
Since I don't want to damage my sounder unnecessarily, and it's pretty much equivalent to a big low-voltage relay, I figured I'd ask the experts for the optimal solution.
Sorry to be so long-winded!
