SP0256-017 schematic

Mentioned on the "Arduino Adventures" page above, I breadboarded this old speech synthesis chip.

It can be a bit pesky to get working, and there are a couple of mistakes in the datasheet that came with the chip, so here's a schematic that should work (and in fact is what I've got on the breadboard).

Click on the image to get the large, original version.


  • note 1: The datasheet schematic had an error here, with pin 20 (/ALD) connected to +5V, in addition to the correct connection along the right side of the chip in the schematic, where it's connected to a pullup resistor and a switch to bring it LOW and latch in the chosen phrase's address from pins A1-A8 when the user presses the momentary switch.

  • note 2: The datasheet also had an error down here, with mention of pin 19, but no name and no connection. It actually should be tied HIGH to +5V in normal use, so that the chip latches in the phrase address when /ALD goes LOW (see corrected connection in schematic above).

  • note 3: The audio amp section is actually optional (the section in dotted outline). The chip itself can drive a small earbud/headphone speaker, or piezo buzzer element directly from the pin 24 digital out. It'll be faint, but it works. For more amplification, add the audio amp section. I assume most any basic transistor or op amp amplifier circuit would work. Also, be sure to test the circuit with a good power supply -- I was getting goofy/no results until I realized the battery I was using to power the circuit was nearly dead...

  • note 4: This is the phrase address section with pullup resistors. So as the schematic depicts them, these pins will be HIGH unless the bitwise switch is closed, connecting the pin to GND and bringing it LOW (logic 0). You could actually use pulldown resistors instead (connected to GND) and have the switches tie them to +5V when closed, which maybe makes more sense, with CLOSED/ON meaning the bit is set to 1. You turn these switches on and off to enable/disable bits in the address to choose the phrase it speaks when you press the pushbutton connected to pin 20 (/ALD). For example, in the SP0256-017, binary "address" 00000000 is "Oh", binary "address" 00001110 (14 in decimal) is for the phrase "fourteen", etc.

For debugging or just for kicks, you can also put an LED between pin 8 and GND to indicate when the chip is waiting for you to enter a new phrase address and when it's finished talking. You can get away without a current limiting resistor in series since the current output of pin 8 (SBY) is low enough.