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Topic: Cheap and simple 7 segment led 4 characters (Read 2187 times) previous topic - next topic

artvolk

Good day!

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)?

Jeff K

Jeff K - JKDevices.com - home of the MegaMini

Onions

My website: http://www.harryrabbit.co.uk/electronics/home.html Up and running now! (Feel free to look round!) :D

CrossRoads

http://www.maxim-ic.com/datasheet/index.mvp/id/1339

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:
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

http://www.sparkfun.com/products/9766

This ready-made module should satisfy your needs. Comes in 4 colors. It's not the cheapest way to solve it, but the easiest.

artvolk

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.

Thanks!

CrossRoads

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.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

artvolk

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?

CrossRoads

Probably, if your 3mA estimate is correct and you are comparing it to having the 7 segment displays on all the time.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


pluggy

#10
Nov 29, 2010, 08:56 am Last Edit: Nov 29, 2010, 09:06 am by stephen_t Reason: 1
The current draw is the reason LED digital watches died in the 1970's  :)

Or maybe not http://www.led-watch.com/
http://pluggy.is-a-geek.com/index.html

artvolk

Thanks for the link, really cool stuff :)

pha555


I recently noted a 4-digit module in Lithuania at

   www.bringyourself.in

I have some code samples at

   http://www.phanderson.com/picaxe/twidisp.html

Peter Anderson

artvolk

Thanks for the response. What MCU is inside this module? Is this AVR or something other?

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