Picaxe Power supply Question
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BeanieBots
Moderator
Yes, as long as you supply the PICAXE via some form of regulator and control the pump via a relay, transistor or other switching mechanism which is tollerant of the pump voltage.
Michael 2727
Senior Member
The MAXimum Output (source) from any Picaxe pin is 20mA.
The MAXimum Input (sink) into any Picaxe pin is 20mA.
And this is at the Picaxe supply voltage level ONLY, usually 3.5V to 5V
E.g. you can't Input (sink) 5V if only using 3.5V as the Picaxe supply voltage.
Any load greater than 20mA and/or above the Picaxe supply voltage 3.5V to 5V should
be driven via a Transistor, MOSFET or Relay-(which will also require a transistor to drive it).
SSRs (Solid State Relays) have an IR LED driving their input side, which can be driven
directly from any Picaxe output for AC switching. ( for advanced users only
)
The MAXimum Input (sink) into any Picaxe pin is 20mA.
And this is at the Picaxe supply voltage level ONLY, usually 3.5V to 5V
E.g. you can't Input (sink) 5V if only using 3.5V as the Picaxe supply voltage.
Any load greater than 20mA and/or above the Picaxe supply voltage 3.5V to 5V should
be driven via a Transistor, MOSFET or Relay-(which will also require a transistor to drive it).
SSRs (Solid State Relays) have an IR LED driving their input side, which can be driven
directly from any Picaxe output for AC switching. ( for advanced users only
)To summarise, yes.
Just to expand on BB's reply.
You should use a 5V regulator to supply PICAXE with power.
If the pump is sensitive you should use a 9V reg to the pump.
Pay attention to the capacitors you will require for the regulators. i.e. look at the regulator Data Sheets.
Don't bodge.
Also, it would be good to put a 47nF - 100nF ceramic cap directly across PICAXE +V / 0V pins.
Take a look in Manual 3 at pages 7 and 9 (std circuits 3 & 4 etc.) to see how you can use transistors/relay to switch the pump.
All this assumes your 'wall wart' is easily man enough for the Pump?
Startup glitches can be reduced with a fat capacitor near the motor relay/tranny, I'll leave others to expand as my beer is getting cold and my mrs is getting hot (I'll have to open the window).
Just to expand on BB's reply.
You should use a 5V regulator to supply PICAXE with power.
If the pump is sensitive you should use a 9V reg to the pump.
Pay attention to the capacitors you will require for the regulators. i.e. look at the regulator Data Sheets.
Don't bodge.
Also, it would be good to put a 47nF - 100nF ceramic cap directly across PICAXE +V / 0V pins.
Take a look in Manual 3 at pages 7 and 9 (std circuits 3 & 4 etc.) to see how you can use transistors/relay to switch the pump.
All this assumes your 'wall wart' is easily man enough for the Pump?
Startup glitches can be reduced with a fat capacitor near the motor relay/tranny, I'll leave others to expand as my beer is getting cold and my mrs is getting hot (I'll have to open the window).
westaust55
Moderator
For a PICAXE power supply capable of being powered from the 9V or 12V pump motor supply see the PICAXE manual (rev 6.6) page 23.
BeanieBots
Moderator
It "decouples" the PICAXE from the motor.
Both motors and micros produce noise on the power supply. By placing capacitors close to the device, it both prevents noise from comming in and getting out. Capacitors are not ideal components. They also have resistance. The resistance is a function of frequency which also depends on its capacitance. Thus, using several capacitors of different value, the capacitors become more effective.
Both motors and micros produce noise on the power supply. By placing capacitors close to the device, it both prevents noise from comming in and getting out. Capacitors are not ideal components. They also have resistance. The resistance is a function of frequency which also depends on its capacitance. Thus, using several capacitors of different value, the capacitors become more effective.
Andrew Cowan
Senior Member
A bit. This means it 'soaks up' spikes, and 'gives out' voltage when there it a drop.
helps keep a signal clean. The larger the capacitor, the larger noise it can filter out.
A big capacitor (eg 100uF) is good at filtering out big noise, such as the power drop when a motor is first turned on. A small capacitor (eg 100nF) (1000 times smaller), is good at filtering out very high frequency noise, such as the interference created by a motor turning.
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helps keep a signal clean. The larger the capacitor, the larger noise it can filter out.
A big capacitor (eg 100uF) is good at filtering out big noise, such as the power drop when a motor is first turned on. A small capacitor (eg 100nF) (1000 times smaller), is good at filtering out very high frequency noise, such as the interference created by a motor turning.
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BeanieBots
Moderator
It is.
An electric motor produces sparks. These produce radio tranmissions and current surges which pass down the power lines. The capacitor absorbs them.
In the micro, every time something switches inside, it draws a very heavy current for a very short time. The capacitor supplies the very short high current. Without it, the power rail would drop in voltage (for a very short time). This can sometimes cause other components on the same power rail to reset or think they have received a digital pulse.
Thinking of them like a rechargeable battery is good analogy.
You also need to think of every bit of wire as a resistor.
It just all happens VERY VERY much faster.
An electric motor produces sparks. These produce radio tranmissions and current surges which pass down the power lines. The capacitor absorbs them.
In the micro, every time something switches inside, it draws a very heavy current for a very short time. The capacitor supplies the very short high current. Without it, the power rail would drop in voltage (for a very short time). This can sometimes cause other components on the same power rail to reset or think they have received a digital pulse.
Thinking of them like a rechargeable battery is good analogy.
You also need to think of every bit of wire as a resistor.
It just all happens VERY VERY much faster.
hippy
Ex-Staff (retired)
The way I like to describe decoupling capacitors across power supply lines and 0V is as 'springs' which will dampen down any shakes ( pulses and dips ) something may induce into the power lines.
They dampen best closest to where they are placed so are usually fitted where interference may be generated ( close to a motor or relay ) or where interference may cause most problems ( close to a PICAXE ).