Bizarre 18X headscratcher

nbw

Senior Member
Hi everyone
I hope you are keeping well during the lockdowns. I've lost my job and possibly relationship, but at least I can use the time to work on some picaxe projects.

I'm seeing the most bizarre thing happening with my old 18X I'm programming. In a breadboard, it's fine to download a simple program. In the circuit board I've made, it says it can't find a picaxe on COM3. When I put the 18X back in the breadboard, it can program it, no issues. I program it to flash an LED, put it back in the circuit board, it flashes the LED. So, I'm guessing it's a download issue of sorts.

I'm using the same power supply, same download cable, same 18X.
Both breadboard and board have pin 4 tied to the 5V of pin 14 using a 4K7 resistor. Both show 5.04V
Pin 2 is going straight to SEROUT on the cable in both circuits.
Pin 5 of the 18X is to 0V, as is the ground pin of the download cable on both circuits.
Pin 3, of the 18X goes out to a 22K resistor. From there, it branches - one to a 10K resistor to ground (checked) and the other to the SERIN of the download cable. Ground to pin 3 of the 18X measures just over 31K on the board and breadboard.

I cannot think for the life of me why both would run a simple program fine, but only one wants to download. I've not only double-checked the download part on the board that doesn't want to dowload, I've actually soldered a fresh one to no avail.

Any ideas???
 

Technoman

Senior Member
Hi,

Did you check from the copper side of your pcb or from the chip side of the socket? It could be a bad solder joint.
 

nbw

Senior Member
Hi,

Did you check from the copper side of your pcb or from the chip side of the socket? It could be a bad solder joint.
Sure did. I actually soldered a fresh 22K/10K set-up away from the original one, still to no avail.

I'm going to reheat pins 2 and 3 on the socket just to be doubly sure though. It must be something to do with those pins!
 

AllyCat

Senior Member
Hi,

I've never used an 18X, but I see that Pin (leg) 4 is marked "Reset", but you haven't commented on that. It probably needs to be specifically tied High or Low to prevent it "floating" unreliably.

Cheers, Alan.
 

Technoman

Senior Member
On the download socket, RXD and TXD are they properly connected ? (above view like in Picaxe manual)

Can you trace the signal, using a scope?
 

nbw

Senior Member
Hi,

I've never used an 18X, but I see that Pin (leg) 4 is marked "Reset", but you haven't commented on that. It probably needs to be specifically tied High or Low to prevent it "floating" unreliably.

Cheers, Alan.
Hi Alan, yes - I have pin 4 -- then 4k7 resistor -- straight to pin 15, and that's connected to 5V. On the breadboard version, I have a 4K7 resistor simply going from pin 4 to the +V rail
 

nbw

Senior Member
On the download socket, RXD and TXD are they properly connected ? (above view like in Picaxe manual)

Can you trace the signal, using a scope?
Hi there, I've modelled the wiring off page 33 of my version of picaxe manual 1. I'm fairly sure they're connected right. From the download cable, I have the 3.5mm stereo plug going into a three-way header - I split that off into ground, serin, and serout. On the breadboard, the serin parts goes to the 22/10K network, and serout goes straight to pin 2 of the 18X. I have the same arrangement on the soldered version. On both, I measure 31K approx from ground to pin 3 (serin).

I don't have a scope any longer (when the wife and I divorced, I needed money so needed to sell some things...). I'm going to the shed now to quickly reheat the soldered pins 2 and 3 of the IC socket, on the offchance there;s a dry joint. Will update soon!
 

Technoman

Senior Member
You don't mention if your PCB is home-made. I would recommend to check the tracks with an ohmmeter.

I have the same arrangement ...
Is a socket soldered on the PCB or are you using the same in both case? A picture could help.
The download socket could be eventually a faulty one.
 

hippy

Senior Member
I have pin 4 -- then 4k7 resistor -- straight to pin 15, and that's connected to 5V. On the breadboard version, I have a 4K7 resistor simply going from pin 4 to the +V rail
Do you mean pin 15 or pin 14 (+V) ?

I would suggest doing an out of board programming adding a SERTXD("Hello") as well as flashing the LED. See if that outputs to the terminal once inserted into the board.

It would be worth posting a photo of both sides of your board as that may reveal the issue.
 

Eng460

Well-known member
I seem to have a talent for that problem or something similar, meaning it all works on the project board assembled from the kit, then not on a board I make from a generic breadboard like printed circuit board.

Each time it has come down the the socket I use for the programming jack.

I have about four sockets in my parts box, and each one has a slightly different pin arrangement, not just on location, but in which pins are the n/o contact and which are the n/c. All the project boards seem to have been supplied with identical sockets, and the boards seem to have the appropriate n/o and n/c pins connected by the track layout.
I now have a spare jack, not connected to a cord and check that I have the right connections when the jack is inserted.

If the above suggestions don’t solve the problem, it might be worth a check.


Eng460
 

nbw

Senior Member
I got the thing working eventually - pins 2 and 3 were dry, from the IC socket to the veroboard. :) thanks!
I have an RBG PWM interesting problem I'll post in another post.
 
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