AP-8 Audio Player Tester

Parallax used to manufacture and sell an Audio Player module designed by the EFX department, which later branched off into it’s own business, EFX-TEK. The AP-8 provided quality audio and amplification in a small format; a format perfect for amateur and professional prop builders alike. If you needed more than eight sounds, the AP-8 was addressable, allowing up to four units to be attached to the same host (serial) connection.

For the Parallax manufacturing team to test each module required a lot of setup and manual interaction. This was very time-consuming and required one to be very knowledgeable with the connections and software. I was tasked with designing a test fixture and test procedure that would automate most of the testing and require minimal setup. The following was the result.

This test fixture provided an LCD display for visual feedback of current test status, as well as a known good module, pre-programmed to provide sounds to record into the module under test. The 4 standoffs mounted above the known good unit were provided to place the unit under test.

STEP 1: The first step in any test procedure is a visual inspection. Part of this inspection is to verify the jumpers circled above were installed properly. The PLAY / REC jumper is then removed for the next step.

STEP 2: The unit under test is placed on the posts (standoffs).

STEP 3: A spare barrel plug is connected to provide power to the unit under test.

STEP 4: There is a special cable with a 4-pin connector which plugs into the 012P pins, all the way to the right (these are the address input and PLAY headers).

STEP 5: The serial interface needs to be connected. This is how the BASIC Stamp module sends commands to the AP-8, and reads responses back. The 3 pins next to this connection allow you to daisy-chain additional modules, but not used here.

STEP 6: The final cable connects to the PLAY / REC pins and has a single white wire. This controls the PLAY / REC mode.

STEP 7: Connect the audio input cable to the input jack. This cable provides the audio to the unit under test.

STEP 8: Connect the speak wires as shown. The speaker used was a repurposed PC speaker (not shown).

STEP 9: The next step was to make sure the 4 DIP switches were all set to the OFF position, the volume control was set at 50% (1/2 way) and the power switch was set to “LO”.

STEP 10: Now the system can be powered on by pressing the red power button.

STEP 11: To verify power, ensure that the green LED on the Super Carrier Board is ON.

The LCD should display the information shown above. Once you see the “PRESS START TO BEGIN”, you know the unit is ready for testing. This indicates a good serial communication with the unit under test.

If for some reason the test fixture cannot communicate with the unit under test, this message is displayed. This may just mean that the connections need to be checked for issues or that there is a power issue. If not, the unit may be bad.

STEP 12: Press the “start” button on the Super Carrier Board to begin testing.

STEP 13: Once testing begins the display will show the status. First the unit will record 8 sounds from the known good unit on the test fixture.

STEP 14: The test person should visually verify that the PWR and REC LEDs are lit. Since the sounds are being recorded in real time, there is plenty of time to check the LEDs before the next phase of the test.

STEP 15: Once the record step has completed, the test fixture will automatically start playback of the recorded sounds.

STEP 16: The test person should both visually verify that the PLAY LED is lit as well as audially verify that the sounds are playing normally. Since the PWR switch is in the LO position, the sounds should play at a nominal volume level.

STEP 17: Once playback has completed the display will ask the test person to change the PWR switch to the “HI” position.

STEP 18: Moving the switch to this position increases the gain on the on-board amplifier, resulting in louder playback. Once the switch has been changed, pressing the start button will repeat playback while the test person audially verified that the sounds play back normally at a louder volume.

STEP 19: Once high-power playback has completed, the LCD will display this message. You have the option to play the messages back again, or start over.

STEP 20: Remove all the wire connections from the unit under test. Unplug the speaker, audio input, control signals and power cord.

STEP 21: Replace the PLAY / REC jumper in the PLAY position and move the PWR switch to OFF. The test procedure is now complete.

For educational purposes, I am including the source code below for download. There is no schematic available, but you should be able to figure it out based on the I/O definitions and the photos. There aren’t that many connections. If you have any questions or are unsure of something, feel free to contact me.

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