mrburnette
Senior Member
Think that PICAXE chip is dead? No scope? What to do?
An old, old trick that I used back in my military days: use a cheap AM transistor radio to "listen" to the sound of your digital circuit. The only criteria is that the radio must have a directional ferrite antenna to help localize the signal.
Tune the radio to the lower part of the AM band and to a frequency that is bot being used for broadcast. You may need to play around with the frequency selection. You will also have to practice positioning the antenna over the digital chip(s) so that you get the strongest signal from the chip of interest. Generally, the radio's rod should be somewhat parallel to the circuit... that is, the rod should not be perpendicular.
Do not wait until you need this trick to use it - practice with a working circuit so that you can recognize the sound of a working circuit. Then it is easier to recognize the sound of a non-working circuit. Digital circuits generate large amounts of square waves at relatively high frequencies and a significant number of harmonics, too. You should also try to practice at different frequencies since the results will 'sound' very different.
Attached is an MP3 of a 30 second recording of an 08M2+ reading the eeprom, doing some math, and then using SERTXD to send the results over COM1 serial.
If you listen carefully, after the initialization sounds there are two passes... the first pass reads the eeprom and does a F --> C conversion and outputs that and then on the second pass, the conversion is C --> F. At the end of the second pass is a wait and after that I halted the PICAXE... you can hear the tone. The BAUD rate is 4800 and the PICAXE is running at the default 8MHz.
Go forth into the closets and basements and find those old AM radios and put in new batteries and have some diagnostic fun. A finely tuned ear is a fine thing.
- Ray
View attachment 11374
An old, old trick that I used back in my military days: use a cheap AM transistor radio to "listen" to the sound of your digital circuit. The only criteria is that the radio must have a directional ferrite antenna to help localize the signal.
Tune the radio to the lower part of the AM band and to a frequency that is bot being used for broadcast. You may need to play around with the frequency selection. You will also have to practice positioning the antenna over the digital chip(s) so that you get the strongest signal from the chip of interest. Generally, the radio's rod should be somewhat parallel to the circuit... that is, the rod should not be perpendicular.
Do not wait until you need this trick to use it - practice with a working circuit so that you can recognize the sound of a working circuit. Then it is easier to recognize the sound of a non-working circuit. Digital circuits generate large amounts of square waves at relatively high frequencies and a significant number of harmonics, too. You should also try to practice at different frequencies since the results will 'sound' very different.
Attached is an MP3 of a 30 second recording of an 08M2+ reading the eeprom, doing some math, and then using SERTXD to send the results over COM1 serial.
If you listen carefully, after the initialization sounds there are two passes... the first pass reads the eeprom and does a F --> C conversion and outputs that and then on the second pass, the conversion is C --> F. At the end of the second pass is a wait and after that I halted the PICAXE... you can hear the tone. The BAUD rate is 4800 and the PICAXE is running at the default 8MHz.
Go forth into the closets and basements and find those old AM radios and put in new batteries and have some diagnostic fun. A finely tuned ear is a fine thing.
- Ray
View attachment 11374
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