Programmer jack warning

geezer88

Senior Member
I searched for this without finding anything, so here's a gotcha on mounting a stereo jack to a conductive chassis. The serial in on the programming cable is wired to the barrel of the plug. On most equipment the barrel is grounded by the jack on a metal chassis. So if you use a metal jack, it has to be mounted on an insulating material from ground. I just found out the hard way. My board worked fine before I mounted it in a metal box where I have the programming jack remoted to the back of the enclosure. Then it didn't. Finally I remembered that the tip of the stereo plug is ground, so the barrel being grounded was shorting out the serial communication.

Is there a rational reason why rev ed used the convention of tip is ground?

tom
 

inglewoodpete

Senior Member
This issue has come up in the past. The cable format dates back to the very early days of PICAXE. Rev-Ed chose an off-the-shelf cable for programming: from memory the cable was originally made to suit a camera. As you have probably seen with many repurposed products: once a standard has been established, in this case by Rev-Ed, it is a business judgement call to make any changes.

I am fortunate enough to have noticed the shortcomings of the cable connections. It is probably why Rev-Ed recommend and market their con039 stereo jack, also available from other suppliers. While the jack's sleeve connection is exposed, the jack does not have a threaded front mount: it needs to be mounted via its pins. I usually use a small piece of stripboard (Veroboard) to support the jack. If mounted in a metal case, I drill an oversized hole for the plug and fit a slim plastic washer between the case and the jack.
 

Attachments

geezer88

Senior Member
This issue has come up in the past. The cable format dates back to the very early days of PICAXE. Rev-Ed chose an off-the-shelf cable for programming: from memory the cable was originally made to suit a camera. As you have probably seen with many repurposed products: once a standard has been established, in this case by Rev-Ed, it is a business judgement call to make any changes.

I am fortunate enough to have noticed the shortcomings of the cable connections. It is probably why Rev-Ed recommend and market their con039 stereo jack, also available from other suppliers. While the jack's sleeve connection is exposed, the jack does not have a threaded front mount: it needs to be mounted via its pins. I usually use a small piece of stripboard (Veroboard) to support the jack. If mounted in a metal case, I drill an oversized hole for the plug and fit a slim plastic washer between the case and the jack.
That is what I did. I oversized the hole in the metal case and used a scrap of lexan to mount the jack.
All is well now. Just wish I had remembered the back*ssward polarity.
tom
 

hippy

Technical Support
Staff member
The cable format dates back to the very early days of PICAXE. Rev-Ed chose an off-the-shelf cable for programming: from memory the cable was originally made to suit a camera
That's correct. This was a standard for digital cameras which used a serial connection to download photos to a PC.

So, when we moved from using a 3-pin 0.1" header as a download connector to using a jack, we simply adopted that standard. It also meant ready made cables were available off the shelf.
 

AllyCat

Senior Member
Hi,

The question arises as to why the "Camera Manufacturer(s)" chose a non-standard connection arrangement. It might be that they wanted to sell their own "proprietary" interface cable at an inflated price (did I hear somebody mention Apples), however, the standard 3.5mm jack socket has a pair of "Normally Closed" contacts on the Tip and Ring, but not on the Sleeve (earth). So perhaps they wanted a "Plug Inserted" logic level relative to Earth, or even to physically disconnect the Earth (supply) rail to some part of the electronics?

This reminded me that originally PEBBLE included the Legacy Header Pins Programming Socket (before my time) but the images have now been replaced by the 3.5 mm jack. However, header pins are quite useful particularly for small circuit boards, so I still use them occasionally and created some new "Legacy" images. Personally, I would have put the Earth in the middle (to make swapping TXD and RXD easy), but both configuratuions allow a standard 0.1" bridge to link RXD to GND if the 10k pulldown programming resistor has been accidentally "forgotten".

The latest version of PEBBLE does still include a section of polarised "Locking Headers", but the images don't appear to be either Locking or Polarised, and of course don't include the programming pin functions. Two files are attached which should just drop onto (overwrite) the .GIF images in the Pebble/Images folder and then (on restarting) the components found in the "terminals" section as "Program Socket Vertical for Stripboard". The overwritten original images are still available in the "Floating" section. I've also created some other component images, but won't offer them yet, until the following issue is resolved:

My component images were created in a very ancient version of Paintshop Pro and have previously worked perfectly. However, my "new" Win10 computer was opening "P_for_FF" in Edge, which seemed to work reasonably well until now. But my substituted images are "invisible" (apart from the "Terminal" name) in Pebble/Edge, even though the thumbnails seem fine in Windows Explorer, etc. (and below). I tried reading/saving the .GIF files through "Paint" but that was worse, still nothing in Edge and the "Transparent" layer attribute was lost in my other browsers. Firefox and Chrome seem to accept the modified files perfectly well, so possibly something for the (very long) Pebble thread?
terminal_135.gifterminal_136.gif

Cheers, Alan.
 

hippy

Technical Support
Staff member
the standard 3.5mm jack socket has a pair of "Normally Closed" contacts on the Tip and Ring, but not on the Sleeve (earth). So perhaps they wanted a "Plug Inserted" logic level relative to Earth
That's what I suspect ...
Code:
                  -.----- +V
                  .|.
                  | |
.----.--------.   |_|
 \  /   /\    |    |
  \/      `---|----^----> Inserted
              |
             -^--------- 0V
Inserting the plug raises the top prong allowing "Inserted" to go high and using the tip means only once the plug is fully in.
 
Top