I want to duplicate the power/sleep LED functionality of an old Apple PowerMac G4 I have. The G4 has a two-color (green/yellow) LED that illuminates a steady green when the computer is on and a pulsing yellow when the computer is asleep. The Apple motherboard sends 3.3V to the LED, switching anode pins depending on the computer state. I now have a mATX motherboard with a 1.5V power LED (PLED) header in the PowerMac case. Below is a circuit I think will work with a PICAXE and the computer. The circuit switch simply illustrates the PLED voltage being on or off as sent by the motherboard. Though it is a rather simple circuit, I have a few questions.
1. In a simulation program, the 08M2 didn’t detect 1.5V on a digital input. I had to configure the pin as an analog input for it to detect the signal. Is that because the 5V (from a USB header) supplying the chip requires more than 2V to be considered HIGH (TTL) and the external 1.5V trigger isn’t high enough?
2. I added a pull-down resistor to the “switch.”
3. The output of the original Apple motherboard was 3.3V but the output of the 08M2 is 5V. Is adding the voltage dividers to get about 3.3V a good idea? Is there a better way to do it, maybe internally in the 08M2?
4. What am I missing that might make this a better circuit?
I have this working on an Arduino but I’m not familiar with the PICAXE. Any help is appreciated.
(I was unable to post a new thread without shortening the title to something rather uninformative. Would be great if a moderator could change it to "Picaxe 08m2 Circuit With 1.5V Trigger.")
1. In a simulation program, the 08M2 didn’t detect 1.5V on a digital input. I had to configure the pin as an analog input for it to detect the signal. Is that because the 5V (from a USB header) supplying the chip requires more than 2V to be considered HIGH (TTL) and the external 1.5V trigger isn’t high enough?
2. I added a pull-down resistor to the “switch.”
3. The output of the original Apple motherboard was 3.3V but the output of the 08M2 is 5V. Is adding the voltage dividers to get about 3.3V a good idea? Is there a better way to do it, maybe internally in the 08M2?
4. What am I missing that might make this a better circuit?
I have this working on an Arduino but I’m not familiar with the PICAXE. Any help is appreciated.
(I was unable to post a new thread without shortening the title to something rather uninformative. Would be great if a moderator could change it to "Picaxe 08m2 Circuit With 1.5V Trigger.")
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