Andreas Spiess video covers voltage supervisors: How to use Voltage Supervisors to protect ESP32, Raspberry Pi, and Batteries
“A voltage detector is handy for projects where you want to make sure your microcontroller doesn’t run at a low voltage. For example, say you have a Feather Huzzah running on a lipoly battery every few minutes. Eventually the battery runs down, and goes below 3.3V, so the voltage to the ESP8266 core is too low, and could cause a lockup or corrupted data. Or maybe your battery is already drained and you’re trying to charge it back up, but as you are trying to charge it up, the Huzzah turns on and the spike of current drains the battery immediately so it never gets through the trickle-charging stage.
This little chip is a simple solution: It monitors the voltage on one Input pin, and when that voltage goes below 3.3V, it will pull the Output pin low. If you connect that Output pin to the Enable pin on the Feather, it will make sure that the Huzzah does not run if the battery dips too low.
The KA75330 starts running at voltages as low as 0.8V so it’ll be the first thing in your circuit that starts up. This little helper can really ease power start-up issues! Works best with microcontrollers and boards that have an Enable pin that is normally pulled high to enable function, and pulled to ground to disable.
This regulator requires at least 2,2uF electrolytic capacitors on both input and output for stability, just make sure your power supply already has those (it almost certainly does)!”
That looks like a great idea and really cheap. If designing my own boards for a production environment I would definitely use it. Some dev ESP32 boards have an enable pin so this would work. Others would not so you would probably have to come up with a power supply cutoff of some sort.
Thank you Sara.
How would you use a TP4056 and a voltage supervisor together for a single cell 18650, solar, ESP32 project?
Previous article: “Power ESP32/ESP8266 with Solar Panels (includes battery level monitoring).” Wanting to add a voltage supervisor and a FET to switch, ESP32 off at low voltage.
Mr. Spiess in his video; on voltage supervisors, he uses a KA75290 voltage supervisor and a IRLZ44N, FET to switch device off at low voltage. How would these components be connected in the previous article diagram that shows Solar cells, TP4056, 18650 battery and LDO regulator?
I don’t have a voltage supervisor to experiment with. So, I don’t know if what I’m saying will work on the solar panel circuit or not. But what I understand is that you want to keep the ESP32 RST button to LOW when the input voltage is lower than 3.3V.
So, connect the voltage supervisor input pin to the input voltage (battery), GND to GND and the output pin to the ESP32 enable pin. When the voltage goes below 3.3V, the output pin goes LOW and pulls the ESP32 enable pin to LOW to prevent it running.
I think you should keep the circuit shown in the tutorial but connect the voltage supervisor input pin to the battery output voltage.
I hope this helps, but as I’ve told you I haven’t tested this.
Would like to turn off the supply voltage to the ESP32 when the 18650 falls to 2.9 volts; which turns off the IRLZ44N FET shutting off the supply voltage to the ESP32. Is 2.9 volts too low for a 18650?
I have a basic schematic; using part of the previously noted tutorial, diagram for illustration. Schematic is untested.
Does schematic look correct?
How can the resistor between Voltage Supervisor and FET be calculated? Believe the resistor between LDO and Voltage supervisor would be a pull-up resistor.
For most 18650 batteries, the working voltage is between 2.5 volts and 4.2 volts. So, 2.9V should be ok.
As for the circuit, I recommend taking a look at the TC54VN2902EZB datasheet. It shows a circuit example for that kind of application: https://ww1.microchip.com/downloads/en/DeviceDoc/20001434K.pdf –> see page 6.
Your circuit seems slightly different. But with circuits there are many ways to achieve the same thing.
I hope this helps and I’m sorry if I can’t help much. I haven’t experimented with that component before and I’m far from being an “expert” in circuits.
Thank you Sara. I have TC54VN2902EZB and IRLZ44N now; now to keep the smoke inside components… I see from the datasheet you referenced in Figure 4.2 (“Other applications”) the voltage supervisor can be directly connected to the Gate of a MOSFET. Will give it a go…
Reviewing Mr. Spiess’s video; this is the circuit for voltage supervisor with a MOSFET:
Voltage Supervisor Battery Cut-off with MOSFET
Will do Sara. Waiting on some components yet to arrive. Miss the time we could purchase components locally.
Found a detailed article on the TP4056.
Updated 10/6/2020; circuit correction.
Breadboarded this circuit; disconnecting Vout of the voltage supervisor at the Gate of Mosfet turns off the LED, otherwise while powered, LED is ON.
Will vary voltage supervisor, Vin to below threshold; this will confirm circuit works as intended. Yet to be done. Looks promising so far…
Voltage Supervisor has a Vdet of 2.9 Volts; which produces a Logic LOW, voltage.
Observation; applying battery voltage of 2.6 volts, LED is “off.” Voltage supervisor causes Gate of MOSFET to switch by sending Logic, LOW to Gate. Applying 3.3 volts to circuit; LED is “on.” This part of the Solar Supply is working as intended.
Results of voltage measurements:
Circuit disconnects load for Solar cell to charge battery using TP4056 and a single, 18650 battery.
Thanks for sharing your results.
It seems that everything is working as expected. Right?
Need to change Vin on Battery Suppervisor to Battery + Out.. You had pointed that out previously; missed that statement. Tested Solar panel this afternoon; panel is outputing 5.71 V. (bright Sun) and 4.15 V. between battery connections (no battery.) Working on getting everything onto strip board. 72 year old eyesight does not help much…
Added two capacitors used in your tutorial.
Congratulations for your project. I would love to see your stripboard once it is ready.
So, if you want to share it here, it would be great!
Keep up the good work.
LDO, Voltage regulator is outputing 3.3 volts. Voltage from Battery + is good at Vin of Voltage supervisor; however, I have no Vout at the Voltage supervisor. Need some time to do more troubleshooting. Will report back.
Sorry for the delay; took time off to visit a sick friend.
Isolated problem to a defective voltage supervisor; replaced with new voltage supervisor. VOut of voltage supervisor is normally a logic LOW, turning MOSFET switch ON, with led ON. When battery voltage reaches 2.9 V. VOut of voltage supervisor becomes a logic HIGH and led is OFF; load has been removed from circuit and TP4056 charges the 18650 battery. Circuit assembly is working correctly…
That’s great news!
I’m really happy that you got it working properly!
And thank you for sharing your work 😀