Digital Voice Modem (audio filter and reference oscillator)
For Two-Way Ham Radio Applications

Documentation for the
INADVM Prototype

Schematic Image.
(Click image to download a PDF copy)

This is a MMDVM (like) audio board called INADVM. The first version of the board is for the Arduino Due. It uses multi-turn pots for receive and transmit audio. The radio connector is a DB9. A 12 MHz TCXO is included. On the board are LEDs for Power, PTT and Data Carrier Detect - (Squelch).

If you purchased our kit, refer to the parts list and make sure you have all of the components you need to build the kit. All of them should have been supplied, but stuff happens!
Click here for Parts List.

Click here for DB9 pin connection assignments.

Recommended powering requirements:
The board requires 5.0 VDC provided by the Arduino DUE.

Explanation of the logic signals and other jumper pins:
The J1 header allows the audio filter op-amps to be sourced by 3.3 or 5.0 VDC. Position "A" is normal, providing 3.3 volts to both filter amplifiers.
If this header is jumped to the "B" position, 5.0 volts are provided to the op-amps and allows the circuitry to have a higher dynamic range and higher output level capability.

The J2 and J3 headers allow testing of the unit when their jumpers are installed. Normally, these loactions are left open (jumper not installed).

The Squelch input requires a logic high, and the PTT output is a logic low.


Email Kevin Custer for ordering information, order by check, and/or quantity pricing of this exciting product.

Product of INAD Communications, all rights reserved.
The INADVM hardware is under KI6ZUM CC license BY/SA/NC
Specifications may change without notice.
Designed by several hams.
Images are property of INAD Communications
Board layout by Kevin Custer W3KKC
HTML as of date below - All Rights Reserved!