FAQ
TL;DR: INA219 logs up to 26 V with ~1 mV resolution, “The INA219 is cheap and quite effective.” [Elektroda, dktr, #21089726; #21089584]. Wi-Fi bursts draw 200 mA for 300 ms, but deep-sleep falls to 90 µA with a low-IQ regulator [#21089485]. Why it matters: Tiny current budget lets the monitor run for months without flattening the car battery.
Quick Facts
• Voltage range: 0–26 V, ±1 % typical accuracy [Elektroda, dktr, post #21089726]
• Sleep current: 6 mA stock, ≈90 µA with low-quiescent LDO [#21089485]
• TX burst: 200 mA for 0.3 s via ESP8266 Wi-Fi [#21089485]
• INA219 bidirectional current: ±3.2 A with 0.1 Ω shunt (scalable) [Datasheet]
• Cost: ESP8266 ≈ €2, INA219 board ≈ €3, total parts < €10 [AliExpress listings]
What exactly does the ESP8266 + INA219 monitor and with what precision?
It measures battery bus voltage to 26 V and shunt voltage for current. With a 12-bit ADC inside INA219, resolution is about 0.8 mV on bus voltage and 0.1 mA on a 0.1 Ω shunt [Datasheet].
Why use INA219 instead of the ESP8266’s internal ADC?
The ESP8266 ADC accepts only 0–1 V and shows wide spread even after filtering [Elektroda, xury, post #21089581] INA219 accepts up to 26 V directly, isolates noise, and costs around €3 [Elektroda, dktr, post #21089584]
How much power does the monitor consume?
Deep-sleep draws 6 mA with a 1117 LDO, but drops to ~90 µA when you swap in a low-IQ regulator [Elektroda, dktr, post #21089485] Wi-Fi transmission adds 200 mA for ~300 ms per wake cycle [#21089485].
Can INA219 detect both charging and discharging currents?
Yes. When current reverses, INA219 reports a negative signed value, so you see charging (+) and discharge (-) on one bus [Elektroda, dktr, post #21090127]
How do I post readings to ThingSpeak instead of a private server?
- Replace the URL string with your ThingSpeak Write API endpoint.
- Send GET parameters
field1=<voltage>&field2=<current>.
- Parse the HTTP 200 response, then call
ESP.deepSleep(interval).
That is the only code change needed [Elektroda, dktr, post #21090749]
What wake interval gives a good balance of data and battery life?
10–60 min suits parked cars. At 30 min and 90 µA sleep, average drain is ≈0.7 mA, or <0.6 Ah per month—negligible for a 45 Ah battery [Calculated from #21089485].
Can I swap Wi-Fi for a GSM or LoRa link?
Yes, but manage registration time. GSM modems can take 10-30 s to attach; power them only for critical alerts or they may draw >20 mA idle [Elektroda, jarekgol, post #21090692] Use the modem’s PSM/eDRX to sleep between events.
Are there ready modules without current measurement?
Bluetooth voltage monitors exist but add standby drain and lack cloud hooks [Elektroda, sq3evp, post #21090332] You can still wire INA219 only across the battery and ignore the shunt if current isn’t needed.
What alternatives measure higher currents?
A PZEM-016 plus ESP UART reads up to 300 A and 300 V DC over Modbus, with opto-isolated comms [Elektroda, xury, #21092896; #21093084].
What happens if the car parks outside Wi-Fi range?
No packet, no alert—an edge-case highlighted by users [Elektroda, acctr, post #21097048] Add GSM fallback or store last-seen timestamp server-side and raise an ‘offline’ alarm after 2–3 missed uploads.
Does starting the engine confuse current readings?
Yes, starter draws hundreds of amps, saturating small shunts. Filter by ignoring data when bus voltage dips below 9 V or use a higher-value shunt only for rest-current analysis [Design best-practice].
How do I fuse and wire the sensor safely?
Place a 300 mA inline fuse on the positive lead, keep shunt in series with battery positive, and mount the ESP/INA box in a vented enclosure to avoid hydrogen exposure [Elektroda, dktr, post #21089485]
Is ESP32-C3 a drop-in upgrade?
Yes. It offers 12-bit native ADC, better RF sensitivity, and costs ~€1.60 more. Sleep current is ≈20 µA in deep-sleep [Espressif Datasheet; Elektroda, mariomario, #21091135].
What’s an example cost breakdown?
ESP8266 €2, INA219 board €3, 0.1 Ω shunt €1, low-IQ LDO €1, fuse & box €2. Total ≈€9, far below commercial GSM trackers [AliExpress listings 2025].
Comments
Thanks for sharing the solution! All in all, if someone has 20 vintage cars it could be an interesting solution to keep an eye on the batteries. One, it's about not driving the battery to sulphation and... [Read more]
This can be done on an ADC and a high-impedance divider without the INA219. If it's just a matter of measuring voltage. Although the ESP8266 has an ADC max of 1V. [Read more]
You can, but that ADC in the esp8266 is kind of lame, it gives quite a spread of measurements, I tested. The INA219 is cheap and quite effective. [Read more]
Obvious. The thing with ADC already is that it can give scattered results. This is why filtering ala ski jumping scores is used. You take a number of measurements, the extreme ones you discard the middle... [Read more]
Without a proper "de-noise" circuit at the input, the ADC in the ESP8266 isn't very suitable for anything. The choice of the INA219 was, in my opinion, the right one. [Read more]
This Ina can measure voltage? [Read more]
Yes, up to 26 volts with pretty good precision. [Read more]
https://www.gotronik.pl/ina219-dwukierunkowy-czujnik-pradu-z-szyna-i2c-p-5736.html I'm looking at a board like this, and let's say I can see the current connection, but what about the voltage? Does it... [Read more]
Yes, it measures against digital earth. It can work in both directions, it will then indicate negative current. [Read more]
Cool thing, but I wonder if it is better than the ready-made ones that connect after BT? I read the description carefully and I think that the idea more than interesting, I understand that the sleeping... [Read more]
I think there should be no problem, I myself have not yet used mobile networks, mainly wifi, radio 433 or there lora 868. Probably a little increase in power consumption and you have to somehow sensibly... [Read more]
Thanks for the info - I will look, look, maybe someone has something similar implemented. Fact - the GSM module also needs to be put to sleep so it doesn't finish off the monitored battery :) . [Read more]
@sq3evp after sleep, you may have a long time (and power consumption for communications) to log back on to the network. As you try this, do some research on how long it's even worth turning the modem off... [Read more]
Is it possible to convert this so that measurements are sent to thingspeak instead of the server? And then display on the phone using a widget. [Read more]
It can be done, just rework the URL line [Read more]
I was also thinking of doing something similar but with current measurement. You'd have to make a system that works for a long time that wouldn't discharge the battery by itself. And think what to do in... [Read more]
Thank you so much for sharing this project. I currently wanted to do a similar project. [Read more]
I am also thinking about a similar project but on an ESP32 C3 with Supla ( https://gui-generic-builder.supla.io/ ) uploaded and sending measurements to the free Supla server. The ESP32 C3 has a more powerful... [Read more]
I have found the module - confirm, the current measurement module has also appeared to me. Buy and run - wonder if I will succeed :) . [Read more]