USB Programming Cable

[pssmith]

I started playing around with PicAxe chips several years back - when every PC came with a serial port. Recently, I needed an axe for a project so pulled some old 18A's out and promptly realised that my main PC has no serial port. Ordered a USB cable from techsupplies, installed the drivers, plugged everything in and ... trouble.

First 08 board I tried it on didn't work, so I tried in on a 40x and it did work. I then wired up an 18A on breadboard and ... it didn't work. I pulled an old 18A board fitted with an HBridge and that did work. I tried swapping various 18 parts into my new board and one of them worked ... once. Having found one reliable board, I used it for the prototype (which is just to drive a small water pump every few hours to water/rinse beansprouts while they grow). An 18 is a bit of a waste though so I ordered some new 08M's. I also googled and read everything I could about picaxe USB problems and searched in here.

The 08M's arrived today so I soldered up one of the little project boards and ... that worked! Flushed with success, I wired one up on breadboard and it too worked! Giddy (almost) with the consistency I tried swapping in the 08M's and checking them, 4 out of the 5 seem to work on the breadboard but one just refuses - it will respond to a firmware check but won't complete a program download.

So, I'm stumped. I suspected some power supply problem but in the last test I did, the power supply didn't change and yet 1 of the new 08M's will not play ball. I presume it isn't dead or it wouldn't respond to a firmware check. I haven't checked yet but I suspect if I plug the same kit into a serial port to program it, it will work.

So anyone any ideas? Is USB known to make individual axes more flakey or intollerant?

 

[Technical]

It sounds like a border line power supply issue, if the supply is dodgy and on the threshold point some chips will work and some won't - try with 4.5V from 3 new AA alkaline cells and see what happens. The USB cable should be more reliable than serial, not less!

 

[manuka]

It's certainly worth a try, as in an otherwise very lucid posting, the power supply is not mentioned. I've NEVER had any PICAXE driving problems with 3xAA ,& even use 2xAA reliably for skin flint operations. A layout picture may help of course, as there could be a blunder with the 10k/22k resistors etc.

 

[pssmith]

It's certainly worth a try, as in an otherwise very lucid posting, the power supply is not mentioned.

It's been varying. 4xAA rechargeables, or other sources (including 4xAA Alkaline, 7.2v Nicad pack, wall wart) via 5v rectifier. In the case of the 08M's, power supply variations were tried but made no difference - hence I didn't provide much detail.

I guess it probably will come down to power supply but IF (and I'll give this a try tomorrow) I can program the same breadboard with the same power supply using a real serial cable BUT the same unit will not program with USB, then the only significant thing that will have changed will be having USB in the chain.

 

[manuka]

Try 3xAA alkalines (~4½V) FIRST! PICAXEs are often confused by even smidgeons of noise on mains sourced PSUs, & of course 7805 regulators are prone to oscillation as well. GO AA !

 

[pssmith]

Try 3xAA alkalines (~4½V) FIRST! PICAXEs are often confused by even smidgeons of noise on mains sourced PSUs, & of course 7805 regulators are prone to oscillation as well. GO AA !

I have to admit to not having a 3xAA battery pack, but can improvise one .

Today I was mucking about with an 08M, the 033 serial LCD kit and an old 28x based robot. Everything was talking but my 7.2v nicad was in need of a charge so I switched over to a wall wart regulated by a 7805. Naturally, it stopped working. I explored various other power supplies - 3xAA Alkaline (fresh), 4x AA rechargeables, various 7805's and an old Farnell variable stabalised variable power supply at various voltages. All failed.

I rebooted the PC in desperation and it's now talking again to the 08M and 28X.

Ho hummm....

 

[Ralpht]

I must admit I have never had a problem with power supplies and Picaxes of various types.
I've used plugbacks (wallwarts) regulated with LM317's, 7805's etc as well as regulate power supplies and have never had a picaxe go into fairyland yet. I tend to use whatever power source comes to hand at the time without thinking about it for longer than - "is it no greater than 5V".

Yes 7805's can oscillate if not set up correctly but getting one to work correctly is trivial. As long as the input/output voltage differential meets the minimum specs and the caps are installed - there is not much to it.

The wonders of modern electronics - what works perfect for one person is a pain for someone else. At least it's not boring.

 

[Ralpht]

Just a thought.
If a mains regulated power supply needs to be used - try putting a 100mH inductor in series with the 7805 / LM317's output after the caps.

Should't take up more room than a 1/2 w resistor. It should help prevent noise spikes from getting through.

I never had the issue but it might help someone else.

 

[sedeap]

Modern Wonders

The wonders of modern electronics - what works perfect for one person is a pain for someone else. At least it's not boring.

Yeah !

The "Manitou" inside the chips and machines, never let one's boring!...

Anyway... that help us (technicians) to earn our way of living. (it isn't only about money)

 

[Ralpht]

Yeah !

The "Manitou" inside the chips and machines, never let one's boring!...

Anyway... that help us (technicians) to earn our way of living. (it isn't only about money)

Yes Sedeap,

It certainly makes life interesting at times

It can't be for the money, it has to be for the love of it
because at least here in OZ, electronics will never help you get rich.