CC2541: 3.3v HM-10 Bluetooth module interfacing with 5v ttl OBD1 Half Duplex ECU.

Archwan K

Part Number: CC2541
Other Parts Discussed in Thread: CC2540

I assume CC2541 is CMOS please review if the interfacing is working. Please advise if any protection needed as the ECU output transistor current can not be much higher than

around 1/2 mA.

Thank you.

over 5 years ago

0 FI over 5 years ago

TI__Mastermind 20800 points

Hi,

Can you share the schematics of HM-10 module?

thanks.

0 Archwan K over 5 years ago in reply to FI

Prodigy 40 points

Hi FI. Thanks for your swift replay. Here is the schematic (stock images). It marked CC2540 but I checked pinouts are the same at least for Tx and Rx.

0 PM over 5 years ago in reply to Archwan K

TI__Mastermind 27145 points

Hi,

Your Resister divider looks OK to me. This will translate from 5 V Level to 3.3V level.

Thanks,

0 Archwan K over 5 years ago in reply to PM

Prodigy 40 points

Thank you PM.

Do we have to actually take into account that 10k pull up resistor inside the ECU output?(circled green) Does that mean we only need 20k resistor out side the ECU to form the resistor ladder?

The second resistor ladder (red side) might not needed since the first 10k/20k ladder has brought 5v down to 3.3v on the anode side already?