ICL7136 thermometer, LED display - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd January 2013, 08:15 PM   #1
diyAudio Member
 
Join Date: Jun 2012
Default ICL7136 thermometer, LED display

I have an ICL7136 3½-digit a/d converter chip and I would like use it as a thermometer. The datasheet features a suitable circuit for measuring temperature with a diode-connected npn transistor.

The problem is that the ICL7136 features outputs for driving a 3½-character lcd screen, while I would like to use two or three 7-segment led displays (common anode) for displaying the temperature. Intersil's application note mentions that the IC outputs ~3.5V(rms) AC for driving the lcd.

Would it be possible to use three ULN2803 Darlington transistor arrays to drive led displays with this chip, like in the schematic?

Attachment #1 shows the circuit I drew with Eagle. It still needs a power supply and another three current-limit resistor networks...
Attached Images
File Type: png schematic.png (48.9 KB, 122 views)
File Type: png Screenshot-2.png (98.9 KB, 120 views)
File Type: png Screenshot-1.png (119.6 KB, 118 views)
File Type: png ULN2803.png (25.1 KB, 117 views)
  Reply With Quote
Old 24th January 2013, 03:54 AM   #2
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
The signals driving the LCD are multiplexed aound the BP output and your design will not work.

Gajanan Phadte
  Reply With Quote
Old 24th January 2013, 08:26 PM   #3
diyAudio Member
 
Join Date: Jun 2012
Quote:
Originally Posted by gmphadte View Post
The signals driving the LCD are multiplexed aound the BP output and your design will not work.

Gajanan Phadte
Thanks for your reply. I have realized that it might be very troublesome to interface an led display with lcd drive circuitry. I need to get an lcd display to use with this chip or use another a/d-converter/display driver IC that has 7-segment led output.
  Reply With Quote
Old 25th January 2013, 07:31 AM   #4
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
If you can accept a display that is not very bright, there is a possibility: you can drive directly LEDs at low current.

To do that, you need a high brightness LED display, one that gives acceptable luminosity at 1mA, a common cathode one, you dimension the segment resistors to give 3 mA and you buffer the BP common with a PNP emitter follower to drive the common cathode.
The peak current in the segment will be ~2mA, due to the internal resistance of the drivers, and the average current will be half of that due to the LCD type drive, but it will work, I have already used such a configuration.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 25th January 2013, 10:01 PM   #5
diyAudio Member
 
Join Date: Jun 2012
Quote:
Originally Posted by Elvee View Post
If you can accept a display that is not very bright, there is a possibility: you can drive directly LEDs at low current.

To do that, you need a high brightness LED display, one that gives acceptable luminosity at 1mA, a common cathode one, you dimension the segment resistors to give 3 mA and you buffer the BP common with a PNP emitter follower to drive the common cathode.
The peak current in the segment will be ~2mA, due to the internal resistance of the drivers, and the average current will be half of that due to the LCD type drive, but it will work, I have already used such a configuration.
Thanks for your tip!
  Reply With Quote
Old 30th January 2013, 04:40 AM   #6
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Use ICL7107

Gajanan Phadte
  Reply With Quote
Old 30th January 2013, 04:43 AM   #7
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
https://www.elfa.se/elfa3~se_sv/elfa...oc=0&q=icl7107 buy it from ELFA.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 30th January 2013, 03:53 PM   #8
diyAudio Member
 
Join Date: Jun 2012
I assembled the circuit on a breadboard. I used a 2N2907A transistor to buffer the 'BP' pin to drive the led displays. I experimented with a 2N2222A signal transistor and also with an MJ15003 power transistors for sensing the temperature. It works very well, although the display segments are quite dim (as expected).
So I may need to try if the display segments could be buffered with some transistors for increased brightness. Or just get the chip which has led segment drivers built-in.
Attached Images
File Type: jpeg imgp3428_v1.jpeg (693.8 KB, 73 views)
File Type: jpeg imgp3429_v1.jpeg (753.3 KB, 17 views)
File Type: jpeg imgp3432_v1.jpeg (592.6 KB, 25 views)
  Reply With Quote
Old 30th January 2013, 04:31 PM   #9
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by d1030180 View Post
Or just get the chip which has led segment drivers built-in.
That's the sensible solution if your display is not bright enough to your taste: adding 23 buffers is not reasonable, unless you have no other choice.
Note that some modern displays can be quite bright with only 1mA average current; yours look like standard-brightness types.

Even a 7107 will not be that much brighter: 8mA instead of 1 looks like a lot, but the eye response is logarithmic, and the BP strobing also increases somewhat the perceived brightness.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 13th May 2014, 12:30 PM   #10
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
So how accurate is this thermometer? I would like to make a simple one with 1-2 degrees accuracy to monitor transformer temperature. Would this design be good for my requirement? Or are there any other simpler alternatives that might do just as well?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
LED display shining through the wood Cassiel Everything Else 12 28th May 2010 12:48 PM
Sheilding from Numerical LED display. henkel Parts 18 22nd October 2008 06:27 PM
Replacing an EL display with an LED one. neutron7 Parts 0 21st June 2008 04:56 AM
WTB: Digit LED display JoshK Swap Meet 0 19th June 2006 04:19 PM
2 1/2 digit LED display bstanton010 Parts 0 14th September 2005 05:30 PM


New To Site? Need Help?

All times are GMT. The time now is 04:25 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2