Problem with Philip Sun Tachometer

[faulcon]

I'm a noobie with electronics and I'm having problems getting the V3.24 of Philip Sun's Tachometer to work.

http://www.geocities.com/ilufa/DST_E.htm

I'm sure I've programmed the PIC 16F84A correctly and have the circuit wired up correctly. I have connected the DB0-DB3 pins on the LCD unit to ground and also tried leaving them disconnected.

All seems fine on power up and the correct voltages are getting to the right places but the LCD unit refuses to power up. I've tried two different LCD units but both stay blank.

Has anybody got any ideas where I have gone wrong??

[Acetronics]

Wrong Contrast setting ??? as 99 times upon 100 ...

Alain

[faulcon]

Wrong Contrast setting ??? as 99 times upon 100 ...

Alain

I don't think it's the contrast. I've got a 10K Trimpot on pin 3 of the LCD and the voltage does vary between about 2.5V & 4.5V when I adjust the trimpot.

Justin

[Chippie]

I had the self same issue with an lcd display bought brand new supplied as a kit for experimenting with....turns out that the voltage on pin 3 needed to be closer to 0v rather than being positive....Some even require a -ve voltage to work....

[Dan Baldwin]

If you had it hooked up as per the schematic, the contrast voltage would vary between 0 volts and 5 volts. My LCD modules need about .7 volts on the contrast pin to work.

Dan

[faulcon]

Hmmmmm......sounds like I might have too much voltage for the contrast pin. I'm guessing that low voltage = high contrast (dark) and high voltage = low contrast (light). I'll try swapping out the trimpot for a different one that isn't a multiturn. This is the current one I'm using:

http://www.jaycar.co.nz/productView.asp?ID=RT4614&CATID=33&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=803

I'll let you all know if it works

Justin

[Zlatko]

Justin,

Multiturn trimpots are fine.

Try to power up the unit without LCD and adjust the trimpot until you get about 0.7V out. Power it off and reconect the LCD then power on. 0.7V for contrast should get you in close, you may only need slight adjustment to achieve the best contrast ( if this is the problem ).

I have seen some spec sheets which were totaly wrong for these types of LCDs ( one of them quoted a contrast voltage of 7V even ... naturally I was scratching my head ... )

Good luck.

[ZAGNUT]

some LCDs have pins 1 and 2 reversed while everything else follows the standard pinout. have even seen one where the data sheet was dead wrong and listed pin 1 as ground when it really is power...




dave

[faulcon]

some LCDs have pins 1 and 2 reversed while everything else follows the standard pinout. have even seen one where the data sheet was dead wrong and listed pin 1 as ground when it really is power...




dave

Yeah, I thought of that but if I swap the power & ground lines won't I risk blowing the LCD?

Justin

[faulcon]

I put the multimeter on the 10K trimpot but couldn't get the voltage below 2.5V. Have just replaced the 10K one with a 100K trimpot and got the voltage down to 0.7V and just like magic the screen started working. Sweet........ :D

Thanks to everyone for their help...I was just about to shove the %$#@*& thing in a cupboard and forget about it.

Thanks again, now I just need to test the tacho with a motor & propeller tomorrow

Cheers

Justin

[Zlatko]

Hi Justin,

Good to see you got it going.

What you are saying about the trimpot sounds strange.
By the schematic, outside ends / extremes are suposed to be 0V and 5V , the slider should be able to adjust to any voltage between 0 and 5 .
Perhaps the trimpot has different pinout or something else is wrong.

Cheers
Zlatko

[elaerico]

Hello, I have a doubth, what pins go connected in the 4013? Because I think that the IC have to be connected to power supply too.