Weak output signal from an external triggering signal

[Teemour]

Hello!

I am asking for help or advice from experienced colleagues. I am developing a device in which the STM32G030C8T6 microcontroller “catches-up” the upstream signal from the 74HC04 inverter with the TIM1 (CH2, as trigger source) timer and should give a pulse on another channel of the same timer (TIM1_CH1, Output Compare). To test the operation of the TIM1 timer, I activated TIM14 as a signal generator and supplied signals to TIM1 (line B) - with such an input signal to TIM1, its output (TIM1_CH1) works as expected and produces pulses with a Vmax above 2 volts. But if I apply an "external" signal from the inverter (line A), then for some reason the signal at the output from TIM1 becomes weak, at a level of 80...120 mV.

[Teemour]

Here are the good output (when TIM14 is triggering the TIM1) and the weak output (when inverter is triggering the TIM1).

Maybe I'm taking measurements with an oscilloscope incorrectly? Or maybe the microcontroller's power supply is not organized properly and this affects the output signal level?

Many thank in advance for your help and advises.

[Sarra.S]

Hello @Teemour, welcome to ST Community, 

some potential issue is that the optocoupler's input (pins 1 and 2) might be loading down the inverter output, causing a weak signal. The input side of the optocoupler typically requires a certain amount of current to operate correctly

Try to temporarily disconnect (U2) from the inverter output and observe if the signal strength improves at TIM1_CH2.