Hi,
We want to measure an unkonwn capacitance using 555 Timer IC (NE555DR) and Schemit Trigger (SN74AHC1G14DBVT). CAP_MEASURE_IN is the unknown capacitance signal to be measured from the and CAP_MEASURE_OUT is connected to MCU frequency pin.
I have supplied 5V to the Timer IC and 3.3V to Schemtic trigger IC. But, my MCU frequency pin is 1.2V level. Please review the connection and provide your valuable inputs.
Thanks.
Hello,
I have checked the standard astable configuration that your circuit is connected in. I chose a 1 nF cap to check the functionality and it operates as I would expect below. I have attached my tina simulation below as well.
Best Regards,
Chris Featherstone
Hi Chris,
Thanks for your support and help for simulation. Our input capacitance range to be measured will be 1nF to 1uF. I hope For 1uF also the circuit looks fine as per the below simulation.
But, I have a concern. I have provided the output of the Timer circuit to a Schmitt trigger before providing to MCU pin. The Schemit trigger VCC level is 5V. So, Can I need to have a level shifter after the schmitt trigger? If required, which level shifter should I use as it has to pass the high frequency signals? Please suggest.
Hi Aakash,
Here is a nice table showing a high level view of some level shifter options. https://www.ti.com/logic-voltage-translation/voltage-translators-level-shifters/overview.html
Alternatively you might be able to use a simple voltage divider to reduce the output square wave to the level you need.
https://www.ti.com/logic-voltage-translation/voltage-translators-level-shifters/overview.html
Best Regards,
Chris Featherstone
