Hello,

Does the usage of the hex inverter in the circuit below look correct? The reason I'm asking is because my first attempt ended up smoking the SN74S04N

I'm using I2C MCP23017 to control a stepper motor driver. The driver IC needs TTL 5V high/low for forward and TTL low/high for reverse. I'm looking for a circuit, maybe a hex inverter, so that I only have to use one high/low line from the MCP23017 to cause the driver IC lines to flip from high/low to low/high. In case you're interested, I'm using the TA7291S/SG driver chip. The logic would look like this: H = H/L L = L/H

Here is a copy of my current circuit, A, which works fine. And circuit B that would only use one line from the MCP23017. Does the usage of the hex inverter look correct?

Any help would be greatly appreciated. Thanks.

 

Looks ok.

 

Looks ok.

Thanks. I'll check my breadboard layout and try again.

 

Does the 74S04 get too hot to touch?
Then you have pins 7 and 14 reversed.

 

Looks ok.

Thanks again. I did try the circuit again and it does work fine now. I'm not sure what I did wrong, I may have not had the VCC +5 to the inverter connected the first time around and it might have back fed through, but it's good now.

 

From the 74S04 datasheet :-

All unused inputs of the device must be held at VCC or GND to ensure proper device operation.

 

Does the 74S04 get too hot to touch?
Then you have pins 7 and 14 reversed.

No. They are correct. But thanks.