Control a obsolete Holtek HT9290A/B DTMF dialer

Figure out how to reliably control a Holtek HT9290A or HT9290B "One-Key DTMF dialer" with a microcontroller, buspirate, etc.

Mike G

Following Follow project

Liked Like project

Become a Hackaday.io member

Just one more thing

To make the experience fit your profile, pick a username and tell us what interests you.

OK, I'm done! Skip

Public Chat

Similar projects worth following

View Gallery

Public Chat

Description

I desoldered a Holtek HT9290A from a old alarm system and tried loading a number into it's registers with various methods to get it to generate DTMF. The HT9290A and B use a 2 wire bus for communication in 5 bit chunks. Thought it would be relatively quick and easy hack.

Initially, I used BusPirate 4 to generate the signals and the HT9290A test circuit from the datasheet on a breadboard. Some success, but inconsistent results.

I switched to an Arduino Nano to have more control over timing and to try to read the data after writing. This led to putting the test circuit on a prototype PCB. Hooking it up to a scope and eventually using extra pins on the Arduino Nano to trigger the scope and give some more debugging information about timing of events.

Inspired by a tweet regarding Ken Shirriff's juror duty.