I designed this gadget mainly for use in industrial and perhaps automotive situations, where a warning or alarm condition can trigger a voice message. This has the advantage that a person doesn't need to look at warning lights etc to instantly know what's happening. The audio amplifier on the board can drive one or more speakers, and there's also a line level output which can feed a PA system or even a radio transmitter.
It's ideal for amateur radio repeater identification and alarm warnings!
The voice messages are recorded into the on-board microphone, then each message can be individually triggered by an external signal. The inputs can respond to simple electrical contacts, logic levels or voltages, and all inputs are debounced to prevent false triggering by electrical noise. Each message can be arranged to play once on a selected change of input state (high-to-low or low-to-high), or to repeat continuously until the trigger condition is removed. These options are selected by DIP switches.
The optional pre-message chime is selected by changing the position of a shorting link, and the on-board relay can switch an external circuit for the duration of the message(s).
Number of messages: One to eight.
Total message recording time: 16 seconds (that's longer than it sounds!)
Individual message durations: Flexible, up to 16 seconds total.
Trigger requirements: Contacts, or DC voltage transition from 0V to between +3V and +20V.
Audio frequency response: -3dB at approx 200Hz and 3.4kHz
On-board microphone: Two terminal electret.
Line level audio output: Approx 200mV RMS.
Output power to speaker: Up to 2W into 8 ohms at +20V supply.
Power requirement: +10V to +20V DC, at less than 250mA on audio peaks.
Relay contacts: SPDT, a couple of amps at 30V DC.
Controls: 'Mode' and 'Record' push buttons.
Dimensions: 5.7 x 3.3 inches (145 x 84mm)
Microcontroller: ZiLOG Z86E0412PSC 1866
No-one's making kits for this circuit now, but you could have a go at making one if you're really keen.
May 2007 update: The ISD1416 recorder chip has been discontinued and is likely to be hard to get. :-(
Click here for the PCB layout as a .pdf file
This can be printed onto transparency film with a laser printer. First do a trial run onto a sheet of paper then measure the pattern to be certain that it's the correct 5.7 x 3.3" size. Adjust your printing/printer settings if required. Alternately, RCS Radio here in Australia can supply the board as part number 95VMA2.
Click here to download the microcontroller firmware file (Checksum = 6A3DH)
The microcontroller needs to be a Zilog Z86E0412PSC 1866 or Z86E0408PSC. It must be programmed with the above file, and for Low Noise operation. A blank microcontroller chip will do absolutely nothing. If you don't understand all this, please don't try to build this project!
If building this project sounds too hard, Ozitronics has voice recorder kits and modules available. Click here to check them out.