TrinitronX
New Member
I've been working on a USB Voltage Delay circuit to delay the enumeration of a certain device on power on and reboot. I use a 555 timer set up to do a single constant pulse after about 11 seconds, this pulse then triggers a PNP transistor to drive the device load.
So far it works fine from a cold boot up state... however, during reboot, the USB bus stays at constant 5V. There must be some data sent over the data lines that tells the device to shut off or reset for a short time though, so the current through the device goes to 0. I need to detect when this happens so I can re-trigger the timer again (set pin 2 to 0), to turn it off and start the voltage delay sequence again.
I've been looking for some sort of current detector I can put in series with the load that won't cause a significant voltage drop. I was going to try to put a LED in series with it and try to use a separate photodiode to detect whether that one was on or off.. but this caused the load to have insufficient voltage.
I was looking at Hall Effect sensors, but it seems most of these are for large currents.. the current through the load under normal conditions stays between 105-112 mA.
I'll attach a schematic and a graph of the current over time during a reboot cycle.
So far it works fine from a cold boot up state... however, during reboot, the USB bus stays at constant 5V. There must be some data sent over the data lines that tells the device to shut off or reset for a short time though, so the current through the device goes to 0. I need to detect when this happens so I can re-trigger the timer again (set pin 2 to 0), to turn it off and start the voltage delay sequence again.
I've been looking for some sort of current detector I can put in series with the load that won't cause a significant voltage drop. I was going to try to put a LED in series with it and try to use a separate photodiode to detect whether that one was on or off.. but this caused the load to have insufficient voltage.
I was looking at Hall Effect sensors, but it seems most of these are for large currents.. the current through the load under normal conditions stays between 105-112 mA.
I'll attach a schematic and a graph of the current over time during a reboot cycle.