Hi everyone,

I want to use ELM327 to work with all types of vehicles, including those with 24-volt batteries.
Diagrams shown in Figures 9 and 12 of the ELM327 datasheet are to work with 12 volt batteries. Although the changes to be made to adapt the circuit to work at 12 and 24 volts may seem obvious, I could not find any info on the rest of the documentation or others websites. I would like to be sure that any changes I make are correct.
I already contact to http://www.elmelectronics.com but they didn't help me very much. I thought maybe someone could give some advise in this forum.

For example, looking at the diagram in Figure 12 my thoughts are:

- LP2950 and LP2951 regulators could be used as they admit up to 30V at the input, although it seems a bit forced.
- The MCP2515 also appears to be suitable for the voltage levels at the CAN bus lines.
- My major concern is with the ISO 9141 interface as I don't know weather to use a high voltage chip interface like L9637 or leave the discrete components. But I think that the issue with the existing components is that the resistors R17 and R19 values should be at least double otherwise the power dissipation would be too high.
- Would have to change the values of R20 and R21 and R34 and R35 so the ELM327 input pins don't exceed 5V, as well as a possible zener for protection.

Any help will be appreciated.

Thanks in advance.