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In my project I need to use
7x tact switches
6x LEDs
3x 7 led segments
1 arduino uno board
my prof says we can use any ICs but arduino uno's pins cannot accomodate all those needed values. I need to manipulate all the tact switches and the 6 LEDs so the only thing that can be reduced is the issue with 7 led segment.
Can you suggest a way that I can reduce the number of pins needed to be used in arduino uno?
For 7 switches , MM74HC164M SHIFT REG 8BIT PISO 14-SOIC
For 6 LEDs and 2 LED digits , (3) SIPO's MM74HCT164MX SHIFT REG 8BIT 14SOIC
For (3) LED digits choose LEDs with BCD to 7seg decoder integrated.
The clk & data lines are shared but a chip selector is needed,.
You can probably reduce the GPIOs usage as follow :
Instead of using 7 GPIOs for 7 x tact switches, you can use a 3x3 matrix for 9 switches : 6 GPIOs
(you can add 2 more tact switches)
Instead of using 6 GPIOs for 6 x leds you can use a 2x3 matrix for 6 leds : 5 GPIOs
Instead of using 21 GPIOS for 3 x 7segment you can put it on a 7 bits bus, and use 3 more pin to control the 7-segment : 10 GPIOs
For switches you need to scan the matrix rows and to know what tact is pushed, and for the led and 7segment you need to refresh quickly, because of eyes afterglow (remanence) the user could not see the flickering/blinking, user think light is fixed on this different leds.
Before : 34 GPIOs
After : 21 GPIOs (With 2 more switches)
You can also consider the 6 leds as a "fake 7segment" ans reuse your 7 bits bus to control them, you only need 1 GPIO to select this "fake 7 segment".
Before : 34 GPIOs
After : 17 GPIOs (With 2 more switches)
Use 'Charlieplexing':
- 6 LEDs can be driven by 3 PINs - see link here
- 7 (up to 12) switches with 4 PINs - see this link, chapter named "Charlieplexing also to interface buttons"
- For 7-segment display I would recommend I2C driven 4-digit LED display (2 PINs - SDA and SCL) - to see available options drop a "7-segment display i2c" line into google.
Total: 3 + 4 + 2 = 9 PINs.
3 x 7 segments and 6 LEDs can be multiplexed with 7 + 4 = 11 pins, in a 4 x 7 arrangement (wire the LEDs as if they were a 4th digit).
If you use 6 diodes with the 6 switches you can share the segment pins of the LED segments, and use one shared input pin (with pull-up) to read the switches.
So a total of 12 pins will be sufficient for a simple (no extra chips required) approach.
Using shift registers or I/O extenders you need even less pins. An MPC23017 for instance requires 2 (I2C) pins and gives you 16 GPIO pins, which is more than sufficient to do everything you asked for. But some programming is required....
