Re: [EE]: Bi-Directional 20A current shunt Using Single supply OPAMP

Hi Justin,

LM324 is ok with directly sensing near GND, but directly sensing near +ve supply 
not so good - input common mode voltage spec 0 - (Vcc-1.5V). Perhaps LTSpice 
doesn't know this. Appreciate the limited parts available, but a specialist current 
sensing chip makes things easy and good. Or a different Op-Amp with rail to rail 
input stage. CGPT suggests TLV2372, MCP6002, OPA2333, TLV9002, LM324-RRI 
(is that last one even a thing?).

Your 2 x diode 1.2V reference workable but not expected to have excellent 
regulation (12.8V supply not precise, temperature effects on diodes). What you're 
aiming for is an offset of around half the 3.3V supply for your uC ADC input... an 
improvement might be a resistor divider across the uC 3.3V regulated rail.

Brent

On 12 Sep 2025 at 10:44, Justin Richards wrote:

> I would like to condition the output of a 1.1mV/A current shunt to drive
> the analog input of a WEMOS D1 Mini (0 - 3.3V).
> 
> The target application is easy monitoring (wifi) of anything 12V with an
> Anderson plug. i.e. Vehicle to Caravan charge line, Solar Panel to Battery,
> Battery to Electric Blanket/Fridge etc.
> 
> The device is to be powered from the circuit it is monitoring which will be
> around 12.8V.
> 
> I am a long way from a bench so have resorted to LTspice.  The attached
> circuit (5KB so I hope it gets thru) appears to behave exactly as desired.
> 
> However, 2 diodes in series to raise the reference to allow for the
> negative swing seems to work in LTspice but I am curious what others think
> about this approach.
> 
> 
> Justin
>