Help for a newbee

[unoduetre]

Hello to all. I'm a total newbee and looking for a good samaritan to direct me .
My problem : the picaxe system looks very interesting and I have bought a 28X1 starter pack. My knowledge of electronics is basic but I am interested in learning (I am 49 y.o never too young to learn eh!). I set up the system and like everybody (i think ) made some LEDs flash just to make sure I didn't burn anything. OK - no problems . I wanted to use the servo (seperate 4.8 Volt supply ) control routine as listed in the manual (see below) - I connected the signal wire (yellow for my Hitec servo) directly to the corresponding out pin on the picaxe chip with 330 ohm resistor (NOT to the 8 Darlington transistor IC).

the manuale proposes this routine

init: servo 4,75 ‘ initialise servo
main: servopos 4,75 ‘ move servo to one end
pause 2000 ‘ wait 2 seconds
servopos 4,225 ‘ move servo to other end
pause 2000 ‘ wait 2 seconds
goto main ‘ loop back to start

my servo just runs fully to one extreme end stop and remains blocked there - it's always the same extreme (doesn't do the servo any good obviously)

I have tried changing the pulse value from 4,0 (not recommended) all the way up to 4, 250 (idem) without any difference

Can anybody make a suggestion - I am almost certainly (without a doubt) doing something wrong but I can't figure out what.
Thanks in advance:

 

[ylp88]

I assume that you've connected the ground/0V rails of your two power supplies together? You have one rail feeding power to the PICAXE and a separate supply feeding the servo (4.5V supply in your case), however the ground rails to the two must be connected together.

ylp88

 

[unoduetre]

hello and thanks for the reply - in answer to your question -yes, indeed I have connected both negative voltages to a common rail but to no avail

 

[Andrew Cowan]

Not all servos go to the extremes of 75 and 225 - do any commands like 100 or 150 work?

Andrew

 

[crossthreaded]

The servo must be seeing a high signal on its input to move at all, if you apply a control of 0v continuously, then they just sit where you left them. So my guess would be that the pin you have conected the servo control to is high all the time. You can confirm this with an LED and series resitor. If the LED is bright (as bright as if across the power rails with a series resistor), then the output pin is high all the time. If the LED is dimmer (actually quite dim), then it may be receiving the servo control signal correctly.

My guess would be either that you have an extra connection to the positive rail on the servo control pin that you are using on the Picaxe, or that you have the wrong pin number. remember that pin numbers and output numbers don't correspond.

 

[catalina]

Not sure what you are attempting with the servo control using the 28X. An 08M would be suitable if just servo testing was required. The attached 08M programme is one I've used successfully for field testing Hitec sail servos. It runs the servo to one end then steps back to the other, verifying the full movements. Give it a try if you feel it is useful.
l

 

[Technical]

We've just tested on our development board with a stndard hitec servo and it works ok - make sure you are using leg 25 (have you used leg 15 by mistake....)

 

[unoduetre]

hello all and thank you for your replies regarding my servo problem - I am out of the country until next Sat so I can't follow up on you advice/s you have given me. Will let you know as soon as I get home and wire up everything as you have suggested. Thanks again. unoduetre.

 

[BeanieBots]

Check that your PICAXE is running at the correct speed.
If you don't have a 'scope to check the pulse widths being sent to the servo, then go back to flashing an LED and check that pause 1000 gives a 1 second delay. If it does not, then check that the resonator is 4Mhz.