ICL7106 and LCD problem - Electronic Circuits Projects Diagrams Free

mabauti · 24th December 2007, 07:08 AM

I have been doing a project using a LCD and the IC 7106. The problem I have is that additional decimal points are showed on the LCD screen, but I didn't connect the respective pins ! ?_? I only connected the first right decimal point.

Maybe some experienced users have had similar problem , that's the reason I posted here this problem.

Circuit attached

any thoughts?

ericgibbs · 24th December 2007, 08:03 AM

hi,
You have to connect the unused decimal point pins to the LCD backplane [BP] pin to switch them OFF.

mabauti · 25th December 2007, 12:48 AM

COM or COM1?

should I connect both COM & COM1?

ericgibbs · 25th December 2007, 08:33 AM

Quote:

Originally Posted by mabauti

COM or COM1?

should I connect both COM & COM1?

hi,
Look at the 7106 pins, see the BP pin, this is the Backplane osc output.OK.

mabauti · 25th December 2007, 09:32 PM

excuse me : should I connect both COM & COM1?

and , just a last question : the LCD reading drifts randomly , e.g. : from 25.8 to 27.4 then 26.9 then 33.7 then 25.4 , etc.

any comments about this?

ericgibbs · 26th December 2007, 09:34 AM

Quote:

Originally Posted by mabauti

excuse me : should I connect both COM & COM1?
and , just a last question : the LCD reading drifts randomly , e.g. : from 25.8 to 27.4 then 26.9 then 33.7 then 25.4 , etc.

any comments about this?

hi,
>>> should I connect both COM & COM1?
I cannot find a datasheet for the LCD??

Do the readings drift when the input probes are shorted together?
Also, how are you powering the 7109?

EDIT:
The connections for generic LCD are shown, its says link commons..

mabauti · 26th December 2007, 07:13 PM

Quote:

Do the readings drift when the input probes are shorted together?

I shorted D1 first, then IN-HI & IN-LO and both drift

Quote:

how are you powering the 7109?

as indicated in the schematic, using a 9V battery. I tried with an AC adapter too (same result)

ericgibbs · 27th December 2007, 08:23 AM

hi,
It looks as though you are using the diode as a temperature measuring sensor???
Where did you get the circuit design from?

Also I dont see any decoupling on your circuit diagram, I appreciate you are using a 9V PP3 battery, but these batteries do have a 'high-ish' internal resistance.
The 7106 will generate some electrical noise on the power rails and you have the sensor diode and Vref/offset connected to that rail.
Connect a 47uF and a 0.1uF capacitor across the power rails.

Have you measured the 9V battery voltage when the circuit is connected.?

mabauti · 27th December 2007, 11:30 PM

Quote:

It looks as though you are using the diode as a temperature measuring sensor???

It was only for schematic purposes, actually I'm using a NPN BJT

Quote:

Where did you get the circuit design from?

Electronics Now , March '95

Quote:

I appreciate you are using a 9V PP3 battery, but these batteries do have a 'high-ish' internal resistance.

I'm using both : rechargeable and alkaline, even an AC-DC adapter

Quote:

Connect a 47uF and a 0.1uF capacitor across the power rails

Done, same result =[

Quote:

Have you measured the 9V battery voltage when the circuit is connected.?

It has a stable reading

btw: the only difference between that design and that of intersil datasheet is the 1Mohm resistor in the zero adjust pot

mabauti · 29th December 2007, 09:30 PM

so what's your conclusion ericgibbs? :

Does the schematic not work (it is wrong)?
should I make the PCB again?

on1aag · 29th December 2007, 10:28 PM

Hi Mabauti,

Try changing the integrating capacitor, the same value but a different
type of capacitor. See if you can find a polypropylene type.
See also page 10 of the datasheet.

on1aag.

kchriste · 29th December 2007, 11:46 PM

How far away is the temperature sensing transistor from the rest of the circuit? Are you using a shielded cable as depicted in the diagram with the shield connected to pin 32 of the 7106?

mabauti · 23rd January 2008, 03:51 AM

It is working now! o_Ô

I did what on1aag1 said, the circuit became more stable, however it still had drifting (pretty much less though). I blame batteries w/o enough charge (I'm using the same batteries I started with)

Quote:

How far away is the temperature sensing transistor from the rest of the circuit?

~10 centimeters

Quote:

Are you using a shielded cable as depicted in the diagram with the shield connected to pin 32 of the 7106?

No at any time.

A new question rises about this kind of IC, from the following schematic

http://www.interq.or.jp/japan/se-inoue/gif/ckt26_11.gif

Question : Will the LCD be burnt because of connecting directly the TEST pin to the DP1?

sachin.kolkar · 15th April 2008, 04:23 AM

hi mabauti,
PLZ send me c code of your time display project.......
i want to introduce this future in my college project........
plz help me............

sachin.kolkar · 15th April 2008, 04:28 AM

hi Kchriste,
Plz send me some C example code for real time clock....
I m using PIC uC .........
PLZ help me boss......

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

24th December 2007, 08:03 AM	(permalink)
ericgibbs	hi, You have to connect the unused decimal point pins to the LCD backplane [BP] pin to switch them OFF. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

25th December 2007, 12:48 AM	(permalink)
mabauti	COM or COM1? should I connect both COM & COM1?

25th December 2007, 09:32 PM	(permalink)
mabauti	excuse me : should I connect both COM & COM1? and , just a last question : the LCD reading drifts randomly , e.g. : from 25.8 to 27.4 then 26.9 then 33.7 then 25.4 , etc. any comments about this?

27th December 2007, 08:23 AM	(permalink)
ericgibbs	hi, It looks as though you are using the diode as a temperature measuring sensor??? Where did you get the circuit design from? Also I dont see any decoupling on your circuit diagram, I appreciate you are using a 9V PP3 battery, but these batteries do have a 'high-ish' internal resistance. The 7106 will generate some electrical noise on the power rails and you have the sensor diode and Vref/offset connected to that rail. Connect a 47uF and a 0.1uF capacitor across the power rails. Have you measured the 9V battery voltage when the circuit is connected.? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

29th December 2007, 09:30 PM	(permalink)
mabauti	so what's your conclusion ericgibbs? : Does the schematic not work (it is wrong)? should I make the PCB again?

29th December 2007, 10:28 PM	(permalink)
on1aag	Hi Mabauti, Try changing the integrating capacitor, the same value but a different type of capacitor. See if you can find a polypropylene type. See also page 10 of the datasheet. on1aag.

29th December 2007, 11:46 PM	(permalink)
kchriste	How far away is the temperature sensing transistor from the rest of the circuit? Are you using a shielded cable as depicted in the diagram with the shield connected to pin 32 of the 7106? __________________ --- The days of the digital watch are numbered. ---

15th April 2008, 04:23 AM	(permalink)
sachin.kolkar	hi mabauti, PLZ send me c code of your time display project....... i want to introduce this future in my college project........ plz help me............ __________________ hm:

15th April 2008, 04:28 AM	(permalink)
sachin.kolkar	hi Kchriste, Plz send me some C example code for real time clock.... I m using PIC uC ......... PLZ help me boss...... __________________ hm: