USB download cable problems AXE027

J

Janne

Senior Member
Hello!

I'm having a problem with the usb download cable. When trying to download/access the picaxe with the usb cable i just get the normal can't connect message. With the connection test button i get 0 and 2.1V with the diffrent lamp settings, i suppose 2.1V measured at serin pin at picaxe isn't enough?

Is there anything else that could be wrong, except the usb cable itself? I'm currently using the AXE090 Experimenter board for testing, with picaxe 18x installed. With the normal serial cable program download works without a hitch.

The problem is that the laptop i'd like to use for programming only has an usb port. As an alternative, would buying a usb-to-serial adapter work?

Thanks for any help you can offer

ps. For the first picaxe project I'm working on a wood fired boiler controller. It's going to control the inlet of air into the boiler, based on fumes temperature. So far I've got the stepper motor interface code working, the stepper will be used to control position of the inlet hatch.(i'm running bipolar stepper with L6219 IC). Next thing is to think some kind of measuring circuit for the PT-100 temperature sensor I have.
 
B

BeanieBots

Moderator
The AXE027 IS a serial to USB adapter so getting a serial to USB adapter won't help.

Your voltage is too low. The question is why?
What is the voltage with just the lead? (ie, not plugged into the AX090)

Have you installed the CORRECT (Rev-Ed) USB driver?
 
J

Janne

Senior Member
Hello BB,

I just measured the voltage from just 3.5mm stereo jack on the usb cable, and it showed 4.5V.. the next thing i'm going to do is to try it with the un-improved download circuit,(ditch the additional resistor and schottky diode) and see if it makes any difference.

Thanks for the tip!
 
A

Andrew Cowan

Senior Member
when people have trouble with the axe027, 99% of the time the problem is with the drivers. Did you follow rev-eds guide to installing it?

A
 
B

BeanieBots

Moderator
Double check your resistors. It's NOT a potential divider but your voltage suggests it might be wired as one.
Although I don't how it could be wrong if you are using a AXE090.
 
J

Janne

Senior Member
I just re-checked the resistors for errors, they seem to be as they should be, and because it works with the normal serial cable it *should* be good right?

As for the drivers, i installed them from the CD that came with the axe090 kit. And because the voltage chages in the plug with the test button, i assume the driver part is working like it should be.
 
hippy

hippy

Ex-Staff (retired)
It sounds like a hardware problem to me.

What voltage do you get on the 22K measured furthest away from the PICAXE, where the signal from USB actually comes in ? This should be around 5V.

Try it with the PICAXE out of the socket and also try the same test in the other AXE090 download sockets; do they give roughly the same ?

I know it's a 'silly suggestion' but check the PICAXE isn't wrong way round, rotated 180 degrees.
 
B

BeanieBots

Moderator
Janne said:
because it works with the normal serial cable it *should* be good right?
Click to expand...
Not true. 'Proper' RS232 voltages are +/-12v. It just happens that a 22k/10k potential divider drops that down to about 5.2v. USB voltages are +5v. The same potential divider would drop that down to about 1.6v. Hence, an incorrect download circuit would work with a serial port but not the USB cable. The 'correct' circuit offers NO divider action.

Anyway, don't see how the AXE090 board could be made 'wrong', so it's probably not that. Could be a wrong value resistor accidentally fitted???
 
J

Janne

Senior Member
Okay I did some more measurements, and also tested it with another picaxe on a veroboard i quickly assembled. Same thing with veroboard, works with serial cable but not with USB.

With the picaxe mounted, I read the same 2.1V on both sides of the 22k resistor(resistor colour codes match 22k, and i measured the resistors i put on the veroboard for added certainity with an LRC analyzer). Again, same on both boards.

But when i removed the axe chip, i got some weird measurements. With the test button "off" i don't read any volts, in either serin and serout. But with the test button "on" I read -4.6V at serial out-pin, and 0V in serin.. This is the same both in AXE090 board and on my new veroboard.

Also just for kicks i tried the test funktion without the picaxe chip and with the normal serial cable, i got +10.5V in serin with the test "on" and -10.5V with the test "off"(with my vero board). With AXE090 the "on" voltage was +10.5 and "off" voltage was -0.2V, clamped by the diode on the improved dl circuit i assume.

Could someone verify the voltages on the usb cable 3.5mm stereo jack? As in, how many volts should i read between the 3 terminals, and which way should the voltage be there? (+ or -)
 
J

Janne

Senior Member
eclectic, yes the resistors in the AXE090 board are in the order you said. Color codes in the resistors match(very unlikely they would differ from the color coded rating)
 
R

Ratty Ma Hatty

New Member
Could it be??

noob post warning, hi all!

I just assembled the AXE090 after many years off the iron and had a problem with my AXE027 USB cable. I bypassed R4 as it was on the SEROUT and my diagram didn't specify it and lo and behold it worked.

Might the reason for the working on the true serial cable be with its higher (~12v) voltages the effect of the resistor pull down still leaves enought for the SEROUT to work however the USB voltage is as previously stated is 5V??

Sorry for the highly technical nature of my post! :eek:


EDIT: Prob best not to connect the true serial cable to your AXA090 after removal of R4, I don't think the PICAXE likes ~12v... :eek:
 
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J

Janne

Senior Member
Update.

I got a 5€ usb to serial converter, and now it works like a charm with my laptop too :) WOOHOO :D
 
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