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PIC TK3 programming and LCDs

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through June 30, 2005 » PIC TK3 programming and LCDs « Previous Next »

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Istedman
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Username: Istedman

Post Number: 12
Registered: 05-2005

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Posted on Sunday, 26 June, 2005 - 11:10 pm:   Edit Post Delete Post Print Post

I have been playing around with PIC Toolkit MK3 this weekend and I have hit a few problems.

I connected my 16 character by 2 line HD44780 based LCD display to the PCB. It worked but the display is faint. I have adjusted the contrast setting on the TK3 PCB but it is not visible face on, but OK at a 45 degree angle. Any suggestions why?

Secondly, I have been trying to use TK3 to program a PIC 16F877 mounted on a PCB of my own design. I have made a programming cable that connects GND, RB7 (data), RB6 (CLK) and MCLR between the two PCBs. The PIC will not program! I get 'No response from PIC' errors. The same PIC programmes/erases fine when plugged into the TK3 PCB.

I have used the 'check PCB' function to toggle the various data lines to ensure that everything is connected properly, it is. Both PCBs are powered, albeit from different supplies but there is a common ground. The programing cable between the 2 PCBs is about 10 CM long. I copied the in circuit programming interface from an EPE design, so I should not have screwed that up ;)

Any help appreciated.

Ian
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Eagre
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Username: Eagre

Post Number: 12
Registered: 05-2005


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Posted on Monday, 27 June, 2005 - 12:09 am:   Edit Post Delete Post Print Post

You do not mention the model of your LCD display. If it is just dim it may be the contrast voltage requirement is outside the 0-5V provided by TK3, or it may be a faulty LCD. Check the LCD manufacturer's datasheet.
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Magnum4
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Username: Magnum4

Post Number: 54
Registered: 04-2005


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Posted on Monday, 27 June, 2005 - 07:21 pm:   Edit Post Delete Post Print Post

Hi Ian.
Re prog chip, I have had problems if RB6 and 7 are not isolated from rest of circuit. Also check if your getting 12v at mclr during prog cycle.
HTH.
Regards,
Jim
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Adam
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Username: Adam

Post Number: 15
Registered: 06-2005

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Posted on Monday, 27 June, 2005 - 09:22 pm:   Edit Post Delete Post Print Post

Ian
Check the supply voltage, they are very fussy with supply voltage. If the voltage is down to even 4.8 Volts you may have problems. Check your code, if you are clearing the screen and then writing the smae thing again it will have the appearance of being dim.

HTH
Regards
Adam
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Istedman
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Username: Istedman

Post Number: 13
Registered: 05-2005

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Posted on Tuesday, 28 June, 2005 - 12:13 am:   Edit Post Delete Post Print Post

Hello,

In answer to a few queries I checked the following.

RB6 and RB7 only connect to a pin header for programming at the moment, there are no other electrical loads. The connection from the programming header is via a 4.7K resistor on each pin. All the correct voltages are present on the PIC, including MCLR going to +12V.

The LCD I have is a Hitachi LM016L and the contrast voltage should be 1.5-5.25V DC, I am supplying it with 5V DC. I halted the PIC (I removed the oscillator) and the display was still dim.

Tomorrow I will check the signals from TK3 to my board using my oscilloscope to look of over/undershoot or other problems.

Thanks for the tips so far.

Ian
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Magnum4
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Username: Magnum4

Post Number: 55
Registered: 04-2005


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Posted on Tuesday, 28 June, 2005 - 01:24 pm:   Edit Post Delete Post Print Post

Hi Ian,
Two points to try.

1) Try prog header without the resistors.
2) put a pot across the supply and the wiper to the contrast supply and see can you vary the contrast.
HTH.
Regards,
Jim
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Istedman
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Username: Istedman

Post Number: 14
Registered: 05-2005

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Posted on Tuesday, 28 June, 2005 - 11:15 pm:   Edit Post Delete Post Print Post

Hi,

I've fixed the re-programming problem, thanks to a few suggestions here.

The CD4053 that drives the signals to the PIC was weak. On the TK3 board it had nice 5V levels. When connected to the PIC on my USB dev board, I barely got more than 2V. Replacing the part fixed the problem. Oh beforehand I had removed the 4K7 series resistors. I replaced these and it failed but I now knew why. I have since changed them to 220R resistors.

The contrast issue I think I have fathomed out. The LCD expects a voltage between 1.5 to 5.25 on the contrast pin. TK3 only connects CX to ground via a 10K resistor! I will connect the other end of the pot to +5V and see what happens.

Anyway that's enough for tonight. A big thanks to you all for your help and suggestions.

Ian

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