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Pocket Calculator Control Interface

Communicating with a TI-83(Plus) or TI-84 Plus

Pocket Calculator Control Interface
Programmable calculators used to be exotic, but now they are standard equipment in almost every school or polytechnic. The TI-83 (Plus) and TI-84 Plus are especially popular. Both models have a ‘link port’ for exchanging data. If you connect the right hardware to this port, you can do much more with it.
Every technician or engineer has a pocket calculator somewhere on their desk. Although the internal processes of these calculators are hardly suitable for control tasks, some of them can be used to build a nice robot.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update
Technical specifications
• 32 ESD-protected inputs/outputs including connectivity for I2C, AVR-ISP, JTAG, RS485 and general I/O.
• Supply regulation using 7805
• Firmware all in C
• Simple to program

Resistors
R1-R5 = 4k?7 (SMD 0805)
R6,R15 = 47? (SMD 0805)
R7-R14 = 1k? (SMD 0805)
Capacitors
C1-C5 = 100nF (SMD 0805)
C6,C9 = 18pF (SMD 0805)
C7,C8 = 10?F 50V
Semiconductors
D1 = SM4007
D2,D4 = 8.2V zener diode
D3,D5 = 4.7V zener diode
IC1 = not fitted
IC2 = ATmega32-P, programmed
IC3 = 7805DT
IC4 = MAX487CSA
PB1-PB8 = LED (SMD 0805)
Miscellaneous
L1 = 10?H
Q1 = 8MHz
PORTB,PORTD,JTAG,ADC = 10-way boxheader
ISP,I2C = 6-way DIL pinheader
POWER,RS485 = PC terminal block, lead pitch 5 mm (0.2”)

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