unstable picaxe28X1

[unlikely]

I have built a controller based around the AXE020 for a 28X1. It accepts and runs programs downloaded to it. However it is unstable and a simple routine that sets 3 outputs say - works for a few minutes then blanks out. ( i have not been able to test the output state as yet). It seems more stable when the serial download cable is connected. Any ideas

 

[eclectic]

U.

Please post your circuit and code.

e

 

[unlikely]

here are circuit description and code

Circuit description

1 4k7 to +V
2,3,4,5 not used
6 22k in series with 10 k to gnd – middle to other side of serial jack
7 to centre of serial jack
8 to gnd
9 ,10 not used
10,11,12,13,14,15,16, 17, 18 – all 10k to gnd
19 gnd
20 +V
21,22,23,24,25,26,27,28 to respectively 8,7,6,5,4,3,2,1 of ULN2803A

Code – just a simple debug routine output a permanent 7 !

let outpins =%00000000
b0=0
main:

b0=7
pause 5000
if b0=1 then one

if b0=2 then two
if b0=3 then three
if b0=4 then four
if b0=5 then five
if b0=6 then six
if b0=7 then seven
if b0=8 then eight
if b0=9 then nine
if b0=10 then ten



goto main:

one: let outpins= %00001110
goto main:

two: let outpins= %00001101
goto main:
three: let outpins= %00001100
goto main:
four: let outpins= %00001011
goto main:
five: let outpins= %00001010
goto main:
six: let outpins= %00001001
goto main:
seven: let outpins= %00001000
goto main:
eight: let outpins= %00000111
goto main:
nine: let outpins= %00000110
goto main:
ten: b0=0
let outpins = %00000000
goto main:

 

[kevrus]

It's worthwhile checking all the connections, not just visually but with a meter for continuity. If it seems more stable with the download cable in circuit, then I would initially look for a dry joint/bad connection on the download part of the pcb, check the 28pin socket also as the 'serial in' does not want to be floating at any time.

 

[eclectic]

U.
I've tried your code, both in simulator and on a 28X1.
It works, but simply outputs on pin 3.

Could you explain further about

"blanking"
and,
if you remove the serial cable, how are you testing operation?

Do you have anything connected to the outputs os the 2803?
e.

 

[unlikely]

pin 7 is connected to the centre of the jack socket WHICH is floating when the board is not connnected to computer, in my setup (just a homemade AXE020 look alike) ! Where does it need to go ? )

 

[BeanieBots]

Serout should be floating when the cable is removed. It's serin you should concentrate on. Make sure that it is held down by the 22k/10k combo even when the cable is removed. Also, double check that the reset input is held high.

 

[unlikely]

oh ! thought i had it then :-(( Serial out is floating and serial in is connected to 10k and 22k chain.
The ULN2803 drives a 4511 CMOS BCD to 7 segment driver, the open collector outputs of the 2803 are connected via 10k 's to 10V. The 4511 is operating at 10V. The display operates from 10V - it is blanking instead of showing a "7".
I have now checked the outputs of the PIC and when it goes unstable the outputs are all set to 0000 instead of 1000. (1000 is required to output a "7" because of the inversion in the 2803.

 

[eclectic]

Simplifying:
What happens if you connect directly to Picaxe outputs 0 - 3?

For example, remove all 10V connections and just connect four LED/resistors?

(Assuming that you've sorted Serin, as BB and Kev mentioned)

e

 

[Dippy]

I take it you've checked the PICAXE o/p pins directly to make sure it's the PICAXE having a funny turn?

Also:-
Is your home-made circuit OK? Stripboard, PCB? Are the tracks OK.
What about your soldering? Are the PICAXE and other chips inserted OK in their ic sockets?
Check with multimeter and give 'em a wiggle.

What power supply type and voltage are you using?

 

[unlikely]

Solved ! It seems there was a dry joint on the wires leading to the display.
I separated the controller from the display and now they have been working separately overnight. Thanks very much everyone for your assistance and helpful advice )

 

[jmumby]

well done, I was going to say you made no mention of decoupling caps.

 

[Dippy]

Excellent, well spotted.

These are always the things to check before posting.
At least you didn't blame a 'faulty' PICAXE like some people have done

 

[jmumby]

........touché