pulse generator with Picaxe.

[Satchid]

Hallo Everybody,


I am using a picaxe 08 and have it programmed to send a pulse out of 0.25 sec and sleep then for 3 seconds. The problem is that a pulse of 4.5 Volt is to low, I preferably have a pulse of 9Volt. This is over the age for a Picaxe.


Now, How can i do it, I need to consume a minimum on power. If possible with 0ne battery.


I can go to an arduino that I can power with 9 volts. But Picaxe consume much less Power.


Wat is the max of voltage that i can put on a picaxe?


PS: this is used to put a voltage on 2 parallel wires around a wooden box like a square foot garden box to keep slugs and snails away from my plants. They are not killed when they touch the 2 wires, but they do not like the mild electric shock and move away not crossing the wires.

 

[Aries]

One way is to use an opto-isolator - keep the Picaxe on 4.5v (it can run on 3, but don't go over 5). The Picaxe side of the isolator is then isolated from what is on the other side, so you can use 9V with no problem. I have some applications using 12V with optoisolators. The one I used was the KB814 which may no longer be available. The HCPL817 looks similar.

 

[AllyCat]

Hi,

The maximum voltage for a PICaxe is about 5 volts (say 3 x Alkaline or 4 x NiMH AA/AAA cells). The way NOT to do what you want is with a 9 volt battery (e.g. PP3/6F22, etc.) and a "78LP05" regulator. The 9v battery has only about 10% of the "Ampere.Hours" of 3 x AA cells (200 mAh v. 2 Ah) and a 7805 will drain much more current than a PICaxe all the time. IMHO a low ("quiescent-") current regulator and/or a switched-mode "Buck" converter (from a 9 or 12 volt battery) is only a partial solution.

Since you only want a pulsed voltage, then the obvious solution is to use a capacitor boost circuit (which used to be known in audio amplifiers as a "bootstrap capacitor", but even in electronics it has now acquired many other meanings). Firstly an output pin (of the PICaxe) would pull the negative side of a large electrolytic capacitor down to ground, whilst the positive side of the capacitor charges via a diode from the supply rail (and a small current-limiting resistor might be desirable). Then the output pin is pulsed high, so the positive of the capacitor must rise to almost twice the PICaxe's supply rail (e.g. 8 volts). That might be all you need, but the addition of more capacitors and/or an inductor gives the opportunity to generate higher voltages (dc or pulsed) with circuits known as switched-mode "Boost" converters, or a (capacitor-diode) Voltage Tripler (or more) network.

Cheers, Alan.

 

[PhilHornby]

PS: this is used to put a voltage on 2 parallel wires around a wooden box like a square foot garden box to keep slugs and snails away from my plants. They are not killed when they touch the 2 wires, but they do not like the mild electric shock and move away not crossing the wires.

Maybe I'm missing something...

Just connect the two parallel wires to a 9V battery. No slug = no current drain.

I was surprised to find that the "electrical resistance of slugs is not commonly documented in scientific literature"

 

[kfjl]

Maybe I'm missing something...

Just connect the two parallel wires to a 9V battery. No slug = no current drain.

That's what I thought.
I like the "no-kill" philosophy of the project, I've been pulling slugs off my radishes for a while now. I put them in the grass a couple of yards away and wait for them to come back. I have a dustbin full of walnut shells I intended to use to make an obstacle course for them, but I think they need my radishes more than I do.
I'd try sticking sand-paper around the boxes.

 

[Satchid]

Thank you all, I will try different setups, and hope it works.
I want to try the circuit without pulse train also. I am only worried for current when it rains, and then the batteries will go low sooner.

Thank you all, i have what i wanted.
Willy

 

[erco]

2N7000 mosfet with Picaxe.

Or 556 dual timer running directly on 9V.

 

[inglewoodpete]

The Arduino chip itself will have voltage limit of 5v. If, as you say the module that you're referring to can run on 9v, then it must have a voltage regulator to drop the 9v to 5v (or 3v). And, if that is the case, the output is buffered with a transistor or MOSFET driver.

 

[Billo]

Id' be tempted to solar power this and use the 556 as suggested by erco.

Solar cell > lithium charge controller > 18650 cell > 3.7V to 9V (or 12V) boost converter > 556 > parallel wires.