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I need some advice with a transistor in a turn signal circuit. Answered

I am working on a turn signal system for a recumbent trike and it isn't working correctly. It's based on your basic 555 timer to provide the flashing. An on-off-on toggle switch will select left or right. I didn't want to be running the 555 timer all the time so I thought I would power it through the switch. D1 and D2 ensure the timer is powered when left or right is selected while only energizing the correct transistor. The visible LEDs will be dash panel indicators and external light clusters will be connected to the jacks. The problem I am having is that both left and right lights flash with the switch in either position. I'm pretty sure that the 555 is actually powering both indicator LEDs on it's own through the bases of Q1 and Q2, instead of just switching them on and letting the current from the switch do the work. I only had generic transistors hanging around and I'm wondering if using MOSFETs would solve this problem? My understanding is that they would not conduct enough Gate to Drain current to power the LEDs.



Best Answer 9 years ago

Looks OK, but there's not the detail in the component values and how the 555 is connected. But if you moved the LEDs to the other side of the transistors (i.e. up the page) you'd eliminate the Gate to Drain current problem L


Answer 9 years ago

Hurray! Look forward to seeing the finished thing L


9 years ago

Are you certain you have the collector, base and emitter wired up right?