I have in mind using an I2C thermostat to turn off a 2809 switch. However, the alert output is a level, not a pulse. I imagine that I could use additional circuitry to cause a level change edge to trigger a pulse, but I’m low on board space and would rather just run the alert line directly to the switch. Is there a config that will let me do this? The polarity of the alert line can be set to active high or active low if that might make a difference.
Also, what are the max and min pulse lengths for the control signals?
The ON, OFF, and CTRL pins on the pushbutton power switch do not require a pulse to operate, but leaving any of them in a high state could interfere with the switch’s other control methods, so we generally recommend using pulsed signals with them. If your alert line can be configured so it is high when you want the switch on and low when you want the switch off, you can connect it directly to the CTRL pin (while leaving ON and OFF disconnected). If you are interested in some other behavior, could you describe it?
Thanks Claire, that’s great. It’s definitely encouraging; it might be worth adding your first sentence to the writeup about the switches on the web page so that users know that there’s a little flexibility regarding control signal timing.
That is almost the behavior I want. Here’s the notional plan.
Power can be turned on with a momentary button push. Config: Connect pin A through momentary switch to ground for on-only operation.
2.Power can be turned off by thermostat alert on overtemp. Config: Direct connect thermostat Alert signal to CTRL signal.
Power can be turned off by external controller after a period of no vibration. Must use I2C to communicate from the external device to this board and the thermostat is the only I2C-aware device on the board. I’d like to use the Alert signal as the switch CTRL, but I’m not too keen on adjusting the high and low limits on the thermostat to force an Alert (nor changing the assertion polarity of Alert in real time) to force a shutdown. Maybe I can find a better way to directly control the Alert signal with this or perhaps a different thermostat.
