555
I've been reading up a bit on the 555 and I'm beginning to see it's brilliance.
Pins
- Ground
- Trigger
- Output
- Reset
- Control Voltage
- Threshold
- Discharge
- Vcc
When the trigger is below 1/3 Vcc, output goes high, and stays high. When the threshold pin goes above 2/3 Vcc, output goes low.
Output can handle up to 200mA.
The control voltage can set the 2/3 level directly. Often it is not used and connected to ground with 10uF cap.
The discharge is a bit confusing. It tied to the collector of a transistor internally. The emitter is tied to the output. So when the output is high, discharge is connected to ground, when output is low, there is high resistance to ground.
Besides the basic modes (monostable, bistable and astable) it can be used for digital logic. The piece that turned me on to this was using it as a temperature controller. Where the 1/3 level corresponds to "turn on the heater" and the 2/3 level corresponds to "turn off the heater". Any logic of that nature.
If a signal is fed into Control Voltage with the circuit in monostable mode, it becomes a class D amp. I'll put this note here, this took me a while to understand; the out put of a PWM encoder, to convert back to analog, needs to go through a resistor and a diode, and there needs to be a cap in parallel with the load.