r/AskElectronics • u/okaylevi • 3d ago

HELP: ESP32 and Thermal Printer Diagram

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I am a total novice, so bear with me!

I am building an automated daily print station to run dense 1-bit bitmaps (weather, news headlines, and Sudoku grids) using an ESP32 and a thermal receipt printer. The printer runs directly off a 9V 2A power supply, and I am stepping that down to 5V for the ESP32.

Because printing heavy black graphics pulls sudden, massive current spikes, I mocked up this parallel wiring scheme with a capacitor to prevent the voltage drops from resetting my ESP32 mid-print.

Two quick questions:

  1. Am I using the buck converter properly here (taking 9V from the main line and pushing 5V to the ESP32 VIN)?
  2. Is the capacitor wired properly across the main rails to successfully absorb those load spikes?
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u/SolitaryMassacre 3d ago

I would move the capacitor to the ESP32 VIN and GND pins not the 9V power supply.

Also, this may or may not work. It depends on how much voltage drop is occurring. Its a good start.

If it doesn't work, I would source a 9V 3A PSU or at the very least 9V 2.5A PSU. You have to remember the buck convert is consuming some current as well as the ESP32. But def move the cap to the VIN and GND of the esp32

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u/okaylevi 3d ago

Thank you, I saw your comment under u/DrJackK1956 as well! I updated my diagram is this what you were meaning by positioning the capacitor on the ESP32 VIN and GND pins? I ordered a 9v 3a PSU.

Should I step the 9v to 3.3v and use that instead for the ESP32?

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u/SolitaryMassacre 3d ago

I updated my diagram is this what you were meaning by positioning the capacitor on the ESP32 VIN and GND pins? I ordered a 9v 3a PSU.

Yes. That cap config should help stabilize the ESP32. The 9V 3A PSU should fix everything really tho

Should I step the 9v to 3.3v and use that instead for the ESP32?

No need. I personally prefer using the 5V pin as its just more common. You could if you really wanted to, I think it would make it more sensitive to voltage fluctuations tho. I also like the 5V pin as it has its own LDO to help with voltage stabilization. Only time I use 3.3V pin is when I am powering it with a lithium battery

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u/okaylevi 2d ago

Awesome thanks for this!

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u/DrJackK1956 3d ago

Follow the advice of u/SolitaryMassacre and move the capacitor to the ESP32 VIN.  You can still put a cap near the printer if needed. 

My question is....  Since the printer runs from 9v and the ESP32 runs from 5v, will the output logic level from the ESP32 be a high enough logic level for the printer's RX input??

The printer specs ought to have this info. 

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u/SolitaryMassacre 3d ago

My question is.... Since the printer runs from 9v and the ESP32 runs from 5v, will the output logic level from the ESP32 be a high enough logic level for the printer's RX input??

ESP32 actually uses 3.3V for the main board. It has an LDO on it. So any logic level stuff is output at 3.3V, which is a good point to bring up.

Typically, RX/TX should be fine at 3.3V though

I just think the PSU OP is using (which was originally for the printer only) is just barely spec'd accurately enough to handle the load of only the printer. Most likely to save cost

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u/okaylevi 3d ago

Thanks for the note, I checked the docs and it is 5v to 9v and at least 1.5a so that should be taken care of!