inverting signal

Thread Starter

vojt444

Joined Nov 25, 2022
9
Hello,
I am making a device with MCP2515 which will be just triggering oscilloscope (using SOF and RX1BF/RX0BF pins) so you can simply see a CAN message from another device with an oscilloscope which doesn't have CAN bus triggering. My problem is that I need a positive pulse to externally trigger oscilloscope which is ok with SOF pin (it just make a puls when the message Start Of Frame comes), but RX1BF and RX0BF pins are inverted... they are normaly HIGH and when the message buffer is full they go LOW so I need to invert this signal. Someone told me something about an easy circuit with MCP602 OpAmp (something like on the picture), but I don't really remember the circuit and how does it work. 602.jpg
 

sghioto

Joined Dec 31, 2017
3,707
You are saying the SOF signal is OK as is but need to invert the RX0BF and RX1BF. Do the RX signals need to be converted to positive pulses and if so what is the pulse duration needed?
 

MrChips

Joined Oct 2, 2009
27,686
What you have shown is a non-inverting buffer.

Move the signal to the inverting input in order to invert the signal. Make R1 = R2 for unity gain in the Inverting Op-amp drawing.

1669394351458.png

Memorize this circuit for all configurations:
1669394532981.png
 

Thread Starter

vojt444

Joined Nov 25, 2022
9
What you have shown is a non-inverting buffer.

Move the signal to the inverting input in order to invert the signal. Make R1 = R2 for unity gain in the Inverting Op-amp drawing.

View attachment 281439

Memorize this circuit for all configurations:
View attachment 281441
Yes, thank you, I didn't realized that I am doing a non-inverting OpAmp.
Forget about my scheme I realized that is wrong. :D
 

Thread Starter

vojt444

Joined Nov 25, 2022
9
You are saying the SOF signal is OK as is but need to invert the RX0BF and RX1BF. Do the RX signals need to be converted to positive pulses and if so what is the pulse duration needed?
Yes, SOF is ok as is. The duration of the pulse is not a problem for me I can change it as I want, because there is another pin INT, which I can connect to the MCU and I can empty the buffer so the RX0BF pin will go low.
My problem is that I need to do the invertor of logic signal on RX0BF... when the pin RX0BF is HIGH (5 V) I need output to be LOW (0 V) and when pin is LOW (0 V) output has to be HIGH (5 V).
 

sghioto

Joined Dec 31, 2017
3,707
My problem is that I need to do the invertor of logic signal on RX0BF... when the pin RX0BF is HIGH (5 V) I need output to be LOW (0 V) and when pin is LOW (0 V) output has to be HIGH (5 V).
If you want to use the MCP602 then I would configure it as a comparator.
1669397439366.png
 
Last edited:

BobTPH

Joined Jun 5, 2013
6,080
What scope are you using? DSO’s can typically be triggered by either a positive or negative transition. Better analog scopes as well, I think.
 
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