Strange Download Problem

[Graham O]

Hi,
I have a 20X2 on a homemade breadboard using the download circuit from the Picaxe manual. (I've made quite a few of these and know that I can follow the download circuit.)The download cable is a serial one coming from a hardware serial port on the PC. Battery voltage is 5V.

When I come to program the 20X2 it gives the message of "Not connected to COM 1, not powered etc." Couldn't find a fault in the wiring so connected a scope to make sure signals were getting to the serial input pin on the chip. As soon as I attached the earth clip to the 0V point on the download socket, the download began and was successful. Without this earth clip, the download fails. Any ideas please?

Thanks in advance,

Graham

 

[eclectic]

Hi,
I have a 20X2 on a homemade breadboard using the download circuit from the Picaxe manual. (I've made quite a few of these and know that I can follow the download circuit.)The download cable is a serial one coming from a hardware serial port on the PC. Battery voltage is 5V.

When I come to program the 20X2 it gives the message of "Not connected to COM 1, not powered etc." Couldn't find a fault in the wiring so connected a scope to make sure signals were getting to the serial input pin on the chip. As soon as I attached the earth clip to the 0V point on the download socket, the download began and was successful. Without this earth clip, the download fails. Any ideas please?

Thanks in advance,

Graham

Graham.
To pre-empt other questions,
can you please post

a. The exact schematic that you are using

b. Two high resolution photo's

of your board.

e

 

[Graham O]

Serial download circuit, Picaxe manual, section 1 page 42. Can't do the photographs tonight as my camera is at work.
Thanks

 

[Technical]

Check all the 0V positions on the breadboard/cable are allcommoned together.
The simple answer is that there must be a bad connection somewhere on your layout.

 

[John West]

Sounds like a missing ground, alright.

 

[Graham O]

That is what I am thinking, but having checked everything many times and confirmed grounding, it is a bit puzzling.

 

[Jamster]

Check the jack soket, sometimes they are faulty on the inside.

 

[John West]

Measure the resistances point-to-point of every connection on the bd. It's gotta be there somewhere.

Also, don't measure chip connections from the solder side, but from the IC pins themselves.

Still no pics?

 

[Graham O]

Finally managed to get back to the board and found the problem lay with the download socket which came from Rev-Ed. The two rear contacts both have 2 pins each and I've only ever soldered 1 on each side which makes it easier to remove if I want or need to. With the particular socket I'm using, soldering all 4 pins makes the download work every time. I had checked for dry joints, but for some reason, there was a poor contact on one side and presumably, the weight of the scope earth lead was bending the board sufficently for contact to be made.

Thanks for your help.

 

[westaust55]

The standard Rev Ed style programming socket with 4 pins at the rear are a stereo socket. The two pins at each rear corner are in fact internally switched.
When there is not plug installed, the internal contact makes and the two pins are conencted together.
When a plug is inserted, the internal "Switch" contact moves and the two pis are disconencted with only one remaining conencted to the stereo plug.

It is totally safe in the programming circuit to solder both pins in each rear corner together but not essential - just use the correct two pins.
Now you have the theory, you can try your multimneter and verify which two pins you must use.

 

[Graham O]

Thanks very much Westaust55. It's amazing what you can learn on here. That is almost certainly what has happened. I've only soldered the outer two pins, so only one was connected when the programming cable was in. I'll have a look at the other programming boards I've made and see how I've soldered those. I've always assumed that the double rear pins were to ensure a strong joint which would not fail after multiple plus insertions.

Thank You.