Picaxe start speed

#1
Hi, I've just put two picaxes (08M) on the same circuit and running the same program (2 lights flashing) and I have noticed that the starting speed is different for each of them. They never start at the same time. Why is this?
 

hippy

Technical Support
Staff member
#3
I'd expect them to start quite quickly ( faster than 2S ) and run fairly close to each other. I've not noticed any significant start-up delays when using 08M's.

Check you've got the correct 10K/22K downloaded interface wired in for both.

Unless there's something peculiar in your program I cannot think why there would be a long start-up time.
 
#4
Oh, I wasn't aware that the download interface was required even when I wasn't downloading something. Is there any way of running it without the download circuit? Can I just connect a 22k resistor and a 10k resistor from serial in to 0V?

Thanks
 
#5
You don't need any download circuit once they are programmed. Just tie leg 2 (the program pin) to ground. Saves 2 resistors. I have at least 20 picaxes all working fine like this.

If the two picaxes are next to each other and there are no filter capacitors on the power supply I suppose theoretically one could start, turn on its led which resets the other one. I presume the power supply has 0.1uF and 33uF-470uF across the 5V.

Edited by - Dr_Acula on 04/09/2007 03:55:28
 
#6
I answered my own question. Putting the resistors in made it run smoothly and start fast :)
Now I've found out the clock speeds are slightly different, but I guess that's pretty common between two picaxes :)
 
#7
Dr_Acula, Could you explain the purpose of the filter capacitors? It SEEMS to be running fine without them.
Also, are you saying I need two capacitors connected to each picaxe? (Sorry, I just don't quite understand how you explained it, I'm fairly new with electronics)
 
#8
The caps are not needed if the picaxe is running low current devices. But say it turns on a led that draws 20mA. And also say the wires to the battery are very thin. The supply will dip briefly and the chip may reset. If the circuit was an audio circuit, like an amplifier, you would hear a click.

Usual practice would be a 0.1uF cap per 3-4 digital chips. These smooth out brief transients. Then you can add a single bigger cap to handle big current dips. For instance, if you were using the picaxe to drive a servo and there was a common supply you would need much bigger caps than if you were lighting a few leds.

So sometimes you don't need these components at all. What I find is that often these sorts of components are available in bulk at really good prices - eg I got a catalogue from a company called Rockby <A href='http://www.rockby.com.au/Rockby/Mailer/010907_1.htm' Target=_Blank>External Web Link</a> yesterday and they are selling 470uF 6V caps for 1c each if you buy 500. So I buy a whole lot and then just mindlessly put them in every circuit. I also have salvaged lots of these components off old computer boards, and I did used to ask myself, if these boards have a 0.1uF for every TTL chip and a 22uF tantalum for every 5 chips, there must be a good reason for that.

Edited by - Dr_Acula on 04/09/2007 05:01:49
 
Top