please forgive me but i'm a total noob to this subject area...
what i'm looking to achieve is to pulse a electromagnet in the 100-200 cycles per minute range with a variable voltage range of between 3V to 9V.
I've been looking around the web for answers and there seems to be a few ways to achieve this..
using the Arduino Uno board and the basic ADC circuit with a potentiometer to adjust the pulse width, however not sure how to vary the voltage? use a relay and rheostat off pin13 ???
also I read that there is a PWM controllers on board, i'm not sure if this would work because i need the circuit to be variable from analogue inputs..
would be very grateful for any suggestions or advice
Thanks
Drippy G
PS. the electromagnet specs are 8x32mm iron core, 8 wraps of 24 gauge motor winding wire.
Well, you cannot pulse such a low resistance coil as that right out of an Arduino pin. You'll need to pulse that through a transistor/s.
I guess you're figuring to vary the voltage ("3-9V") to vary the field, but that could be effected through duty (pwm). You could analogRead a pot and vary pwm based on that.
like i said, total noob too this, i understand the pulsing part with a potentiometer...
but the variable voltage configuration is something i can's seem to get my head around..
lets say i ran a separate circuit consisting of..
9VDC battery
rheostat
electromagnet...
this would give me a variable voltage/field,,,
to tie this in with the pulse part you mentioned a transistor, would that be connected to a digital output on the Arduino and the above circuit to act as a switch??
again, please excuse my ignorance, having only had my head in this for a couple of weeks makes me a complete dummy in this realm. What I have learned so far is from wikipedia and youtube..
to tie this in with the pulse part you mentioned a transistor, would that be connected to a digital output on the Arduino and the above circuit to act as a switch??
Transistor or Transistors - Yes!
You get that with a low voltage (3V) you have a weaker field and than with a higher voltage (9V).
Likewise, a low duty pwm results a weak field and a higher duty pwm results a stronger field.
** Pulsing a coil is fun: because you get to learn about inductive reactance! **
You could also smooth out the pulses to effect a variable DC, too.
Before you can decide what transistor is suitable, you need to find out what current the electromagnet takes. The simplest way is to measure its resistance when cold and then calculate the current at the highest voltage you intend to drive from. If the current is more than 500mA then use a logic level n-channel mosfet. Otherwise a bipolar npn transis will suffice.
Normally, you should connect a diode across the electromagnet to catch the back emf when the current switches off. However, this diode slows down the current decay in the electromagnet, and as you are switching it at around 2 or 3 times a second, you may need to get a faster current decay. The easiest way to achieve this is to put a resistor in series with the diode. For example, using a resistor of the same value as the resistance of the electromagnet will halve the decay time, at the cost of doubling the voltage seen by the transistor or mosfet.