First breadboard PIC project problems

U

UmBongo

Member
I have been trying to build my single digit 7 segment DS18B20 temperature circuit on a stand alone bread board and have experienced a very strange problem...

Components:
PICAXE: 18F14K22 - 20X2
DS18B20 - temperature sensor (with 4.7K resistor on the data pin)
Kingsbright SC08 11EWA 7 segment display (using 1K8 resistors)
- see http://www.alldatasheet.com/datasheet-pdf/pdf/233140/KINGBRIGHT/SC08-11EWA.html for data sheet.
Breadboard
3xAA1.5v power supply

When I run the chip on the AXE-091 using the on-board 7 segment display and DS18B20 it works fine.

But when I put it on a bread board like (without the programming circuit)http://www.picaxe.orconhosting.net.nz/20m7segds.gif
I had the following problem/s.

The circuit runs for 3 seconds then switches off. When I disconnect the battery supply and try again sometimes it works, but only for 3 seconds.

I tried every combination that I could think of to try and isolate the problem.

I put the chip back on to the dev board it and worked fine.

I changed the code to:

Code: 
main:

	let dirsB=%11111111

	let pinsb = %11111111

goto main
and just tried to drive normal LEDS with 1.8k resistors on the breadboard. Sometimes the LEDs would light up and if they did it was only for 3 seconds.

I put power directly to the resistors feeding the LEDs (bypassing the chip) and they lit up fine. I even tried to only drive 1 LED in case I was trying to draw too much power through the PIC and it still did not work.

I did the same for the Kingsbright display and it lights up fine (run power directly through the feed resistors with no PICAXE involved).

I found that that when I put the chip back on the breadboard and did not press it in all the way the LEDs lit up sometimes, and if I 'wiggled' the chip up and down it slightly it would sometimes light up the LEDs without being pressed down all the way. So I though the breadboard may be defective. I tried a new breadboard and I had the same problem.

I kept on checking the chip on the dev board at every stage and it always works fine.

This is my first standalone PIC circuit and I am sure I am missing something obvious! :) But I have tried to follow a process of elimination to try and work it out for myself, but just can not work out what the fault might be....

(I have pulled the components from the breadboard - if a picture is needed I can put it back together and take one if it helps).
 
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W

westaust55

Moderator
without the programming circuit
Click to expand...
When you do not have a full programming circuit wired to the PICAXE chip, you must hold the SERIN pin low still. Best to do this via a 10 kOhm resistor to 0V.

No resistor and if the SERIN in pin floats high then the internal firmware (permanent program) thinks you want to download a new program and stops the currently installed program running.
 
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D

Dippy

Moderator
Read Manual 1 and the text under each "MINIMUM operating circuit" for each PICAXE.

Don't worry, many of us have made the same mistakes :)
 
U

UmBongo

Member
The 10K resistor worked. The circuit is now a stand alone project!!!

This is a first for me and I never thought I would get there, so thanks everyone :D
 
W

westaust55

Moderator
great to read that you have it working now.

It really is worth reading those manuals thoroughly, although there is no mention of exactly why it does not work if the SERIN is floating - but now you know.

EDIT:
Likewise, on PICAXE chips with a reset pin, that pin MUST be pulled high for the program to run.
 
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B

boriz

Senior Member
“The circuit is now a stand alone project!!!”

Very pleased for you. The feeling of achievement you get when ‘a plan comes together’ can be a powerful kick, almost like a drug. Picaxe is great isn’t it :)
 
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