ATtiny85 Electronic Load

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1. Overview

TinyLoad is a simple electronic constant current dummy load. The ATtiny85 measures voltage, current and temperature of the heat sink, calculates power, energy and battery capacity, controls the fan and displays all relevant data on the OLED. The button is used to switch between power/restistance and energy/capacity display.

Project Video:


2. Calibration

The ADC of the ATtiny does its best to make the tinyLoad a pretty accurate tool, but it might need a little calibration.

How to calibrate:

  • Set ULCAL and ILCAL to "1" in the sketch, compile and upload.
  • Choose a stable input voltage of around 5V and turn the poti until the display shows a current of around 0.7A. Measure the voltage and the current with a trusty multimeter or a good lab bench power supply.
  • Calculate the calibration factors as follows:
  • ULCAL = voltage measured with multimeter / voltage shown on OLED.
  • ILCAL = current measured with multimeter / current shown on OLED.
  • Set the ULCAL and ILCAL value in the sketch, compile and upload again.

3. Notes

  • Use a good heatsink with a 5V fan for the MOSFET !
  • Be careful with high power loads ! This device is called "tinyLoad" for a reason !
  • Always turn the POTI full counter-clockwise before connecting the load !
  • Due to the input offset voltage of the OpAmp the minimum load current is 17mA.
  • The maximum load current is 4.5A, however for small voltages it might be less.
  • Do not exceed the maximum voltage of 26V !

4. License


This work is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported License. (


Tiny Load



ID Name Designator Footprint Quantity
1 1N4148W D3 DIODE-SOD-123 1
2 SI2302 Q2 SOT-23_L2.9-W1.3-P0.95-LS2.4-BR 1
3 KF301-2P TEST KF301-2P 1
4 LMV358 U3 SOP-8_150MIL 1
5 OLED OLED1 I2C OLED 0.96" 128X64 1
6 5V1 D2 ZENER-SOD-123 1
7 100k R8,R7 0603 2
8 10k R12,R11,R1,R9,R2 0603 5
9 1k R13 0603 1
10 47k R10 0603 1
11 IRL540NPBF Q1 TO-220-3_L10.0-W4.5-P2.54-T 1
12 5A F1 F1206 1
13 ATtiny85 U1 SOIC-8_208MIL 1
15 1u C3 0603 1
17 3x6x2.5 RESET,SET KEY-3.0*6.0 2
18 100n C5,C1,C6,C4 0603 4
19 47u C2 1206 1
20 10k R6 RES-ADJ-TH_3296X-8MM 1
21 Header FAN,NTC HEADER_2X1 2
22 R300 R3,R4,R5 2512 3
23 SS54 D1 DIODE-SMA(DO-214AC) 1


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Comments (2)

johngr Reply

hello.hope you're ok...i was looking to built a li ion capacity meter and found this project .can you set the cut off voltage of the battery to be tested and leave it discharging and measuring the capacity of the battery? i have a lot of 18650 laptop batteries and a chinese module i have i dont think is very accurate. will this project do the job?thanks!!

Stefan Wagner Reply

@johngr Hi, this will not work in the way you want. The load is controlled by the poti, not by the MCU. What you can do is connecting the battery to the electronic load via one of these cheap protection circuits, they have a fixed cut off voltage depending on the protection chip. However, for a much better solution take a look at my Power Analyzer project which can offer all you want:

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