Now, onto trying out a circuit. The bottom-right of the diagram in Direwolf's Raspberry-Pi-APRS.pdf looks like this:
Testing this out is pretty simple. I centered everything on a 2N2222. I then wired the 2.7k resistor (plus an LED, to give some visual indication that it's working) to a DPST push-button switch, to +3.3vdc (coming off an Arduino, because I had one handy :). The PTT line I ran through another LED and another resistor (4.7k, in this case) to the same +3.3vdc rail on my breadboard. The ground line, of course, went to the ground rail. Push the button, both lights come on, and Bob's your uncle.
The point of doing this is a) because it's easy and rewarding, at my (basic) skill level, b) it proves that I have a (working) transistor, and c) that it won't fry at +3.3vdc. I mentioned in an earlier post that I needed some stuff from Jameco, and with their $20 minimum (at least without a hefty surcharge), I wanted to know that I have the basics.
What I'm missing, and will have on order very shortly, are:
- A GPIO breakout for the RasPi. This device will let me connect all of the pins on the RasPi to a breadboard, and make it very easy to play with all the components.
- A 6-pin DIN cable. The Yaesu CT-39A cable is $20; the 10' male-to-male cable off Jameco is $4, which means I'm one snip away from *two* CT-39A's, if I need them.
- A 6-pin DIN socket, to be able to connect the cable (and hence the 8900) to my breadboard. (I hope; looking at the datasheet, it might not be as simple as plugging the socket into the breadboard, but at worst, I can solder leads to the socket pins, and go from there.)
- A CMOS 555 timer chip, which is the center of the other 90% of the circuit in the pdf (and a ceramic capacitor pack, because I don't seem to have any below 1uF).
- A breadboard, because if I get it to work, I'll likely want to not take it apart. (Which is also me saying I'm not yet up to designing a PCB, to make this permanent, but maybe we'll get there someday... one step at a time...)
No comments:
Post a Comment