ICL7106 and LCD problem

[mabauti]

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.

**broken link removed**



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

Circuit attached


any thoughts?

 

[ericgibbs]

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

 

[mabauti]

COM or COM1?

should I connect both COM & COM1?

 

[ericgibbs]

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]

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]

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]

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

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

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]

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]

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

Where did you get the circuit design from?

Electronics Now , March '95

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

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

Done, same result =[

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

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[mabauti]

so what's your conclusion ericgibbs? :


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

 

[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.

 

[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?

 

[mabauti]

Re:

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)

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

~10 centimeters

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

**broken link removed**

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

 

[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............

 

[sachin.kolkar]

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

 

[Nalle]

Hi Kchriste

Im building a circuit using the diode as a temperature measuring sensor incuding 7106IC and LCD. But I cant figure how to connect the LCD pins to the IC pins as in circuit diagram it has one big arrow incuding all pins. Please help me...

 

[Nalle]

hi mabauti

Im building a circuit using the diode as a temperature measuring sensor incuding 7106IC and LCD. But I cant figure how to connect the LCD pins to the IC pins as in circuit diagram it has one big arrow incuding all pins. Please help me...

 

[mabauti]

you can get the connection pins by downloading the 7106 datasheet; and for the LCD may be this can help ya :
LED Display - 35LCD (3.5 digits)