Dumb newbie questions

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brillig99

New Member
Hi Guys,
Excuse my complete ignorance of matters electronic....a retired mechanical engineer with only a vague understanding of Ohms Law and binary averse, but always ready to learn a new subject.

I had a PICAXE 18 pin tutorial board for Chrissy and I have a few questions arising.......

1. The literature bangs on about 4 AA cells for power but the board was supplied with a 3 cell battery box.......how come?
2. Can I assume that an output going 'high' receives battery voltage or is it a conditioned reference voltage derived from battery voltage?
3. On the tutorial board where does the adc reside .....in the PICAXE chip or elsewhere?
4. I have a rare collection of brushed pager motors and others that I can run from a pwm drive signal on the output pins but I cannot find the current limit of the driver chip? Anyone got a clue.....I do not want a visit from the smoke fairy.
5. Has anyone managed to run a brushless motor from a PICAXE chip? If so can you share your experiences?

Regards Ian
 
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BCJKiwi

Senior Member
Hi and Welcome.
Can answer some of your Q's right off - but first (if you don't already have them) download the three Manuals - they should be installed along with the programming editor - click on Help and browse through manual 1 getting started, and 3 interfacing.

1. Max safe working voltage on the PICAXE is 5V so current practice is to use 3 1.5V cells not 4. It is VERY IMPORTANT not to apply more than 5V!
2. Outputs will receive 5v minus an internal protection diode drop so will be around 4.5 V. Inputs will accept 5V but the chip will see a lower voltage than that as a 'High'
3. The 18X has three ADC ports built in. All PICAXE chips have at least one built in ADC function. These are available only on certain pins as they are a function of the internal hardware of the microprocessor.
4. The boards use the ULN2803A. This has a maximum of 500mA per output but they can be paralleled up to increase the output. If the loading is high then it may get hot - take care.
If you have the high power version of the board then it has four transistors on it capable of 10Amps (but would require heat sinks if the load is high).
5. Sorry - don't have experience with motors.
 
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Rickharris

Senior Member
brillig99 said:
Hi Guys,
...

1. The literature bangs on about 4 AA cells for power but the board was supplied with a 3 cell battery box.......how come?
Click to expand...
Use to be 6 volts but some of the familly will overheat at 6 volts so the "standard" is 4.5 volts now. Manual out of date in some places.
2. Can I assume that an output going 'high' receives battery voltage or is it a conditioned reference voltage derived from battery voltage?
Click to expand...
Yes the outputs provide supply voltage more or less. max 20 Ma - do not exceed supply voltage to an input either.
3. On the tutorial board where does the adc reside .....in the PICAXE chip or elsewhere?
Click to expand...
ADC done in picaxe chip. readadc 8 bit resoloution or readadc10 for 10 bit
4. I have a rare collection of brushed pager motors and others that I can run from a pwm drive signal on the output pins but I cannot find the current limit of the driver chip? Anyone got a clue.....I do not want a visit from the smoke fairy.
Click to expand...
as answered 500 mA for the single output 2803 and you can put 2 in parallel see interface manual.
5. Has anyone managed to run a brushless motor from a PICAXE chip? If so can you share your experiences?

Regards Ian
Click to expand...
The brushless motor is essentially a stepper motor, the picaxe may notrun fast enough for you to get any real speed out of it. A command takes something in the order of 200 micro secs to action.
 
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inglewoodpete

Senior Member
Ian does not mention which board he has. If, like me, he is using the CHI030 board, then you can use 1 or 2 supplies. The board can be run from 6v: there is a 100ohm resistor (R9) to drop the voltage between the 6v side of the circuit and the PICAXE part.

Personally, I use 2 supplies. I have removed the 100ohm resistor as described on page 2 of the CHI030 document. I use a 5v regulated bench supply for the PICAXE and 12v for the output devices. The PICAXE could also be run with 3xAA=4.5v.
 
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brillig99

New Member
Thanks guys, my CD would not run for some strange reason and I did not get manuals 2 ,3 which explains stuff in much more detail. This has now been downloaded from the Picaxe website and I feel much more confident.

All tutorials completed without major mess up. Currently working out the components needed for a brushless motor run timer for a free flight for a model aircraft with a dethermaliser, roll and pitch trim and motor speed control.

What an amazing bit of kit the Picaxe system is when complete electronic dumbo's like me can manage it without much ado.

Regards and thanks again , Ian
 
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manuka

Senior Member
Ian- where are you? I've a stash of ultra low current 4 wire steppers, thanks to an Electronic Goldmine special, & still have a few left (although presently buried during a workroom revamp!). These drew only ~15mA & as a party trick could be run directly from a PICAXE-08M. See => http://www.picaxe.orcon.net.nz/stepdemo.jpg Stan in NZ
 
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Michael 2727

Senior Member
If you keep to the adopted rules of -
5V MAX Supply voltage, no ifs buts or maybeys.
(unless you have Trade or Cert papers to know better)
5V MAX input/supply to any other Picaxe Pin.
MAX 20mA Sink (pin used as NEG) or Source (pin used as POS)
Any load over 20mA you must use a Transistor or MOSFET.
Always use a gate or base resistor for the above.
Serin Pin must never be left flaoting.
( 10K to NEG resistor or the Standard Download Circuit )

You will keep the Smoke inside the Picaxe package ;)
 
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armstronginoz

New Member
Brushless motor control for model aircraft

Funny you should mention this as I've been trying to achieve something similar. Simple soul that I am, I've been playing with the servo command on an 08M with the motor connected via a Hyperion ESC. Using variations of code frags I can make the motor run, but not to my satisfaction. Single speed with a regular, brief hiccup repeated ad nauseum. I was looking for an opportunity to ask if anyone has any suggestions(polite).
 
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D n T

Senior Member
motor going brrrmmm, hic, brrrmmm

Just a couple of fishing questions...
Are you using "pwmout"?
Have you tried bypassing the hyperion ESC dodad, because the PICAXE should be able to do the job, although you may have to go through a mosfet, see the interface and command manuals for more info.
Have you used the PWM wizard to get you frequency up above say 20 Kilohertz ( I think thats right, must check)
More details on the HIC,
Have you tried connecting and LED in parrallel to see if you can see the HIC?
Could you show us the code you are using and we might be able to assist in the editing.

I hope this helped, I've been through what you are now but I ended up going to a brushed motor for $$$$ reasons

Do Tell.
 
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