I need to use 4 character 7 segment for my project. Even with dynamic indication it takes too much pins and too much code. Is there any option to get controllable over serial or I2C (or anything else) 7 segment?
Can it be cheaper than 16x2 character display (less than $9)?
MAX7221, very easy to write to with SPI
Can control from 3 to 8 seven segment displays.
1 resistor sets max current, 16 levels selectable via software.
Request a sample, or purchase for $4.
Easy to wire up to common cathode 7-segment displays.
All segments wired in parallel, unique common cathode to each device.
Writing to its registers:
// MAX7221: write shutdown register
digitalWrite(SS,LOW); // take the SS pin low to select the chip:
SPI.transfer(SHUTDOWN_ADDRESS); // select the Address,
SPI.transfer(0x00); // select the data, 0x00 = Outputs turned off
digitalWrite(SS,HIGH); // take the SS pin high to de-select the chip:
This ready-made module should satisfy your needs. Comes in 4 colors. It's not the cheapest way to solve it, but the easiest.
Thank you for the quick responses and for a big number of options I now have.
Have I understand it right that 4 character 7 segment will draw more power than average 16x2 LCD (1.5-3mA)? I'm building battery powered project, so this is critical.
Would have been nice to know that at the start.
The current draw for the LEDs would be under your control - both how long you turn them on for, how bright you drive them.
I don't imagine they'd be too bright with 3mA multiplexed over 28 segments.
So it seems 16x2 is more power efficient if I need to keep 7 segment on (or scan repeatelly -- depends on the circuit) and to be readable like 16x2 display with backlight turned on?
Probably, if your 3mA estimate is correct and you are comparing it to having the 7 segment displays on all the time.
The current draw is the reason LED digital watches died in the 1970's :)
Or maybe not http://www.led-watch.com/
Thanks for the link, really cool stuff :)
I recently noted a 4-digit module in Lithuania at
I have some code samples at
Thanks for the response. What MCU is inside this module? Is this AVR or something other?