How important is the programming jumper?

abenn

Senior Member
I used to mount my 08M2 devices in a socket, so that I could remove them for programming on my PICAXE proto board (and because I was scared of damaging them while soldering!), but for some while now I've been mounting them direct to my project PCBs and adding a programming socket and a jumper, exactly as on the proto board.

But how important is the jumper that disconnects the serial out 0 pin from the rest of the circuit when programming? In my circuits serial out 0 is usually connected directly to an input pin of a Darlington array device, or via a resistor to the base of a transistor. Do I really need to be able to break this connection while programming? If not, I can reduce my PCB board sizes slightly by eliminating the extra header pins for the jumper.
 

Technical

Technical Support
Staff member
As long as you do not mind the output device that is connected to the darlington driver pulsing on and off during programming you can leave the jumper off.
 

hippy

Technical Support
Staff member
Whether the jumper is needed or not really depends on what is connected to Output 0. Output 0 will have a varying output when downloading a new program which may be undesirable and adversely affect attached hardware. The jumper is there so the output drive can be disconnected rather than having to disconnect the hardware.

We would recommend always using a socket for the PICAXE so it can be more easily removed if it ever has to be, but it is your choice.
 

abenn

Senior Member
Thanks for those replies. In my applications the output hardware (servos or LEDs) is always disconnected for programming, so sounds like I can omit the jumper.

As for the socket, I've just started using the SMD version, so socket is not possible :) Anyway, I like the lower profile that is achieved when using no socket with conventional components.
 

hippy

Technical Support
Staff member
Good point; there's not a lot of choice for SMD!

One trick for 'having but not having' the jumper is to include the holes for a 2-pin header on the PCB but have those bridged by a track. The bridging can then be cut and a header soldered in if it ever turns out to be required or desirable.

That won't help though when aiming to minimise board size.
 

abenn

Senior Member
Good point about including the holes but not the header. For my current project the board width is determined by the 8-pin by 2-rows output header, but omitting the jumper pins will certainly make it less bulky even though I still need 6 input pins (3 for Rx connection and 3 for the programming lead). By the way, I've got an adapter lead from the programming lead's jack plug to a 3-pin plug, so I can install a less-bulky 3-pin header on my boards for programming, instead of a jack socket.
 

grim_reaper

Senior Member
I was looking a headers the other day, and thought you may not know that you can get some very narrow pitches these days!
The smallest "usable" one I saw was 1.27mm.
Might save you a tiny bit more PCB!
 

hippy

Technical Support
Staff member
I was thinking; it might be possible to put the header holes under the PICAXE chip or under some other components. Not to solder header pins into, but allow a 'hold against pins' contact to be achieved when programming. Zero increase in board area if there is space for those holes and they can be routed.
 

abenn

Senior Member
Thanks for those ideas. 1.27mm headers might be a good idea for my programming lead, so there can't be any confusion with the normal 1/10" (2.54mm) headers I use for connecting servos and LEDs. I'll look for them next time I'm ordering components.
 

WHITEKNUCKLES

New Member
Greetings Abenn,

We may have discussed Picaxe servos on another forum.

I use a 3.5mm socket to a Molex 3 pin plug and socket (as the original Picaxe download) to 3 probe clips.
The board is intended to allow 4 RC servo outlets 2 to standard RC pins on the right and pin/sockets removed from turned pin IC sockets on the left and top centre for download input.
These Pin/sockets are more compact than standard.

In the photos the lead to the left is a Radio control input lead soldered under the board as is the .1 capacitor.
The bare board is drilled and if it would be of interest to you I would be happy to send it to you.

Dave
 

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abenn

Senior Member
Your screen name doesn't ring a bell with me, but I do visit a couple of RC aircraft forums and have discussed PICAXE there in relation to lighting circuits and, maybe, something to do with servos.

I'm not really desperate to reduce my board sizes, but I think that the idea of having the holes or pads on the board, but no pins attached, sounds like a good way to make things more compact. Developing your idea a little further, why not just have three header pins, spaced well apart so that probe clips can be attached to them, but cut down to, say, only 2mm high? Looks like they'd be less intrusive than the sockets you've got.
 
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