Hi. I am trying to make a circuit that will detect forward and backward motion. It will use two 555 timers, 2 laser sensors, and 2 transistors. This is the way it will work:
If Timer 1 is triggered first, it will output a positive charge to AND gate #1 and AND gate #2. It will also hold the second timer's output low on AND gate #1. Once Timer 2 is activated, it will output a positive charge on AND gate #2. So AND gate #1 is (High, Low) and AND gate #2 is (High, High). So AND gate #2 will output a positive charge. (If timer 2 is activated first while timer 1 is activated afterwards, then AND gate #1 will be High). I use the 2 transistors to sink the current on one terminal of each AND gate.

The problem is when I try to simulate it in Ltspice transistor spikes on the collector and base of both transistors. The spikes only occur when the second timer is triggered (not the first). Can you get transistor voltage spikes if you apply voltage to the base while the collector is grounded?

Here is my schematic

 

hi 464,
What was your .tran on that simulation.
BTW, 200K is very high for Base resistor.
E

EDIT:
Please post a complete asc file, showing the trigger signals.

 

This is the circuit with the .trans simulation.

I have also included the waveform for the voltage spikes

 

hi 64,
Downloaded your post #3 info, will look it over.
This asc file is a alternative circuit, check it out.
E

 

hi,
Checking your circuit shows these are low level transients on power up and are due to the way your circuit is configured.
eg: both 555 Trigs are held Low, there is a long power up delay on the 555 reset pins.

You are still showing 200K Base resistors, why have you chosen 200k.??

You should try to simulate the trigger signals for the 555's as expected from the actual sensors.
E