Sierra

Radio

© Sierra Radio Systems

HamStack Project Pack

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.

Rear View

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.

DB9 RS-232 serial data jack.

2.1mm coaxial DC connector for power input.

Power supply - The project board uses a switching regulator to allow a very wide range of voltage inputs up to the typical 13.8v power found in ham radio stations.  The switching regulator allows for large voltage drops without the voltage regulators overheating.

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 - The supplied LCD display will plug directly into the 10 pin header connectors.

DTMF Decoder - The 8870 DTMF decoder chip takes receiver line level audio input and will decode the presence of all 16 DTMF digits.  Sample programs will display decoded characters on the LCD display or send them to the serial port.

Tone Generator - The CPUs pulse width modulator (PWM) circuit is used to digitally generate audio tones that can be used for a variety of purposes from code practice oscillator to bench top audio tone generator.  The output of the PWM is fed through a 5 pole low pass filter to shape the waveform and filter out high frequency components.  The audio level is adjusted with the on-board (blue) pot with the little knob on top.

3 Reed Relays - The built-in reed relays provide silent, fast switching up to 500ma.  The reed relays are ideal for keying transmitters, passing audio signals, or just about anything that needs isolated switching.

Temperature Probe jack - A 3 pin connector and pullup resistor is available to directly plug in a HamStack temperature probe which uses the DS18B20 digital thermometer chip.

Features

• 2 digital inputs with 10k pull up resistors to +5v DC
• 4 analog inputs with a selectable  voltage range of 0-5 or 0-22 volts DC
• 3 high speed, quiet, SPST reed relays capable of switching up to 500 ma.
• 1 opto isolated digital output
• 1 RS-232 serial port
• 1 analog signal output that can generate a sine wave 0-5kHz at 0-5v DC
• 8870 DTMF decoder chip
• 1 Temperature probe input
• 3 additional general purpose CPU IO connections
• 5v DC power supply (supply rail for logic and analog chips)
• 2.5v DC power supply  (bias supply for op amps)
• 3.3v DC power supply  (supply rail for 3.3v parts)
• 5 pole low pass filter to condition the analog signal generators output

Top View - Without CPU board.

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 0-5v DC.  With the voltage dividers jumpered in, you can scale up to 22v DC.

Documentation

Project Board Manual

Builder’s Alerts

CW Keyer App Note

HamStack

Project Pack