© Sierra Radio Systems
The CPU board plugs on top of the project board.
This picture shows the project board mounted in the plastic chassis box. The front edge provides many convenient IO connections including power in, DTMF decoder audio in, test tone audio out, 4x analog inputs, 3 SPST reed relay dry contacts, and 4 uncommitted CPU pins.
The rear connectors include...
RCA connected to an opto isolator for digital output. Ideal for transmitter CW keying.
3.5mm stereo jack for audio tone output. Used for test tone generator and other projects.
10 pin header connector for ribbon cable to LCD display.
3.5mm stereo jack for 2 digital inputs with pullup resistors. Ideal for CW paddle input.
2.1mm coaxial DC connector for power input.
Power supply -
The power supply delivers 5v DC for logic and analog chips. 3.3v DC for new generation digital and analog chips. 2.5v DC voltage reference used as a bias voltage for op amps when powering the with a single ended +5v DC power supply. These voltage are delivered on all stacking boards through the interboard connectors.
LCD Display -
DTMF Decoder -
Tone Generator -
3 Reed Relays -
Temperature Probe jack -
Top View -
You can see the DTMF decoder on the left side and the 5 pole low pass filter op amp on the right side. The one surface mount component is the 3.3 v DC voltage regulator just under the DTMF decoder. It is a very easy part to solder to the board. The jumper block under the op amp, is used to insert the voltage dividers into the analog inputs. The default range of the A/D input is 0-