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Programmable calculator

The ET-58 calculator is a clone of the TI-58/TI-59 programmable calculator from Texas Instruments, with an ATmega328P processor. The calculator is offered as a commercially sold kit (offered e.g. on Aukro). The descriptions given here are primarily intended as instructions for building and using the kit. The calculator firmware is not included, it is only supplied as part of the kit. However, the ET-57 calculator firmware is freely available (for the ATmega88 processor), with which this calculator will work as a clone of the TI-57 calculator (the source code of the ET-57 is given below).

user manual in Czech language: ET58_User_Manual_CZ.pdf
instructions on how to build the calculator in Czech language:
drawing of component layout for mounting:

--------------------- other downloads ---------------------

user manual partially translated into English (to page 71): ET58_User_Manual_EN.pdf
manuals in PDF and DOC format:
source codes of the embedded library module:
plexi in DXF format:
schematic and circuit board for Eagle Free (note, C1 change to 220 uF!):
graphic documents (schematic, circuit board, keyboard):
source codes of ET-57 clone for ATmega88:





List of properties:

Power supply voltage 2.5 V (from battery) to 5.5 V (from USB connector).
Calculation accuracy 19 digits
Data display up to 14 valid digits
Exponent 4 digits, range +- 9863
1000 user program steps in EEPROM (program storage even without battery)
110 data registers
16 HIR control registers
Two-line LCD display (2 x 16 alphanumeric characters)
45 buttons
Calculator code completely written in AVR assembler
Built-in library with 50 programs and almost 10000 steps in length
Exponential and logarithmic functions
Trigonometric functions
Hyperbolic functions
Factorial of decimal and large numbers
Random number generator
Index access to variables
Indirect parameters of functions
Scientific and technical display mode with exponent
HEX, OCT and BIN display, including decimals
Bitwise AND, OR, XOR, NOT, shift operations
Pseudographic display of graphs and pointers
Program display of text
Dynamic keyboard input at runtime
Statistical functions and linear regression
Absolute addressing, labels, relative jumps
Calculations with matrices
Complex numbers
Evaluating polynomials
Numerical search for roots of a function
Numerical calculation of integrals
Interpolation and approximation
Calculations of triangles
Unit conversions
Circular section
Combinations, permutations
Floating diameter
Interest and repayments
Time conversions, time zones
Interval between dates, day of the week
Games (Hi-Lo, Codebreaker, Acey-Deucy, Lander and others)
Astable Generator with 555
Reactance of capacitors and inductors
Serial and parallel ordering of components
Active and passive filter calculations
Signal convolution
Discrete Fourier transform
Ohm's law
Number sorting and the median
Finding prime factors
Finding the minimum and maximum of a function
Measuring reaction time, stopwatch


The ET-58 calculator has one known defect based on the characteristics of the processor that must be taken into account (and is therefore not subject to complaint). The processor operates at 4 MHz. At this frequency, it is unable to oscillate at supply voltages lower than approximately 2.2V. The processor uses brown-out detection, which resets it at voltages lower than 2.0V. It may happen that if the processor power supply gets into the 2.0 to 2.2V range, the processor may freeze because its clock does not operate properly with this voltage. This can occur both when the battery is very weak, and when the battery is tampered with, where the supply voltage may briefly fall into the forbidden 2.0 to 2.2V band.

Therefore, if you ever find that the calculator becomes inoperative even though you connect it to an external +5V power supply (can happen when handling a weaker battery), disconnect the external power supply, remove the battery and leave the calculator without power for a few minutes. After a few minutes, connect the external power supply, the calculator should boot up properly. For these reasons, it is better to handle the battery with the external power supply connected. You can reduce the necessary waiting time of several minutes by shorting the electrolytic filter capacitor in the power supply (this is able to maintain the calculator's state when the power is off for several minutes).

List of components:

- 1 piece, Microcontroller AVR ATMEGA328P-PU SDIP28
- 1 piece, HT7533-1 TO92 HOLTEK fixed voltage regulator
- 1 piece, LCD alphanumeric display 16x2 characters, yellow-green, HD44780
- 1 piece, Unipolar transistor IRLML6402PBF SOT23
- 3 pieces, Schottky diode BAT42
- 1 piece, Ceramic Capacitor CK 22n/50V X7R 10% RM5.08
- 2 pieces, Ceramic Capacitor CK 100n/63V Y5V RM5.08 +80/-20%
- 1 piece, Electrolytic capacitor CE 220u/10VT JAM-TK 5x11 RM2.0 BULK (5x11 mm)
- 1 piece, USB-MINI B F SMD connector
- 1 piece, Battery holder for PCB BKC3003P
- 45 pcs, Microswitch TC-0108-T
- 1 piece, S1G20 2.54mm pin strip
- 1 piece, Metallized resistor RM 100R 0309 1W 1%
- 1 piece, Metallized resistor RM 2k2 0204 0.4W 1%

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