...and here is the huge comment that made the sketch too big to include in a forum post.
Regulated DC Positive Voltage Booster
Created 12/17/2008 by Amp <firstname.lastname@example.org>
Modified 11/28/2011 to be compatible with the newest Arduino IDE 0023
If powered by the Arduino 5V, connected by USB it should be reasonably safe to
build and operate this circuit if you follow the guidelines provided below.
There is some risk of personal injury. (read the disclaimer)
Voltage Input: +1VDC minimum, 12V maximum
Voltage Output: Vin to +60VDC maximum
Output Power: 250mW maximum (0.25W), dependent on Q1, L1 and voltage source's internal resistance
Using 5V from the Arduino, at 250mW the input current drain is 50mA (0.25W/5V=0.05A).
10V circuit output, max current is 25mA (0.25W/10V=0.025A)
20V output, 12.5mA max (0.25W/20=0.0125A)
40V output, 6.25mA max (0.25W/40=0.00625A)
THE #1 RULE: Do not charge large capacitors to high voltages.
Capacitors can discharge instantly, and that can be hazardous.
Voltages exceeding 60V may be possible
* Wear safety glasses
* Don't lean over your circuit while it's powered
* Don't wear loose fitting jewelry
* Keep liquids, flammable or loose debris away from the circuit
* Do not leave the circuit operating unattended
* Never power the circuit from negative voltages, AC or directly from a wall outlet
Inductors resist changes in current. When Q1 is active, a larger current begins to flow through L1 to GND.
When Q1 is switched off, the current through L1 trys to remain the same as it was, causing an increased voltage.
By varying the PWM duty cycle, the current through L1 can be controlled.
A larger duty cycle makes a larger output voltage.
Regulation is important when the output load isn't constant.
If the duty cycle remains the same, and the load increases, the output voltage will be reduced.
The software senses changes in the output voltage, and adjusts the PWM to compensate.
The output voltage depends on load and input voltage, which are "unknown" variables, so the
mathematical relationship between PWM duty cycle and output voltage are "guessed" by the program.
If the input voltage and output load were constant, the Arduino analog input wouldn't be necessary.
With regulation, almost any load and input voltage can be used to make an accurate output voltage.
An "unregulated" positive or negative voltage booster can be built with a 555 timer, instead of the Arduino.
A negative voltage booster is possible, but Arduino analog inputs need positive voltages.
Sensing and controlling a negative voltage with the Arduino can probably be done with a depletion mode MOSFET/IGFET.
That would require negative "Aout" tied to the gate of the dep. MOSFET, with +5VDC (current limited) tied to the source.
With proper biasing, -1VDC would be +4VDC, -2.5VDC = +2.5VDC, -5VDC = 0VDC, so invert the measurement (1024-measurement)
This is an untested suggestion/idea. I'd be surprised if this is all there was to it.
*Follow the safety rules above, before proceeding.
1) Assemble and check the circuit components, without the Arduino connected
Power Up Check (DO NOT connect PWM pin 9, or ADC pin 0 until instructed to)
2) Connect Arduino GND to circuit GND (this is called common ground)
3) Connect Arduino 5V to circuit voltage input (the voltage input of L1)
4) Measure circuit Voltage Output is less than 5V (minus the D1 voltage drop), and more than 0V (check inductor)
5) Measure circuit analog out (Aout) voltage is less than 400mV (5V/15=0.333mV, Aout is a 15:1 voltage divider)
Power Down Check (still, do not connect pin 9 or 0)
6) Disconnect 5V, your circuit output voltage will gradually fall to 0V
Never disconnect GND, unless every other wire to the Arduino is already disconnected.
(always connect GND first, and disconnect it last)
7) Repeat the power up check again, and then move on to Operation.
8) Choose a low voltage in the setup routine below, such as 9 (where "power_level=SetVoltage(v)" chooses the voltage)
9) Connect ADC pin 0 to circuit Aout (between the 1.5M and 100K resistors, where shown in the schematic)
Make sure pin 0 is connected correctly, or your output voltage wont be regulated.
10) Attach your Voltmeter to circuit Vout
11) Watch your Voltmeter while you connect pin 9 to the circuit PWM (disconnect pin 9 if the voltage is wrong)
You can turn off the voltage booster by disconnecting pin 9 from the PWM
All power can be shut off by disconnecting pin 9 (first), and disconnecting Arduino 5V
Do not disconnect GND. (see step 6)
Shut off the circuit before touching, removing or replacing components or wires (see above, and step 6)
P) At step 4, the voltage wasn't between 0V and 5V
Check diode D1 is inserted with the correct polarity, your inductor is securely connected and conducting,
NPN transistor Q1 is connected according to the schematic (collector to L1, emitter to GND)
P) At step 4, the voltage was 5V
Check your diode D1 is inserted correctly (5V minus its voltage drop, is what you should be measuring at Vout)
P) At step 4, the voltage was above 5V
You skipped my instructions and wired arduino pins 0 and 9 already, shame on you.
P) At step 5, the analog out voltage was above 400mV
Your resistor voltage divider is not wired correctly (check 1.5M and 100K resistors weren't swapped)
P) At step 5, the analog out was 0V (or open and floating)
Check the voltage divider is wired to the circuit properly, and the resistors are not "open" (damaged)
P) At step 5, the analog out voltage was changing constantly or I got no reading
Make sure the Arduino GND is connected to the circuit GND, and see the above problem about open/floating voltage.
P) After step 9, the voltage dropped slightly
Your inductor doesn't have enough turns (A PWM frequency of 62KHz isn't high enough)
P) After step 9, the voltage increased only slightly
The inductor doesn't have enough turns, or your transistor (Q1) isn't working right
P) After step 9, the voltage increased beyond the chosen voltage by more than 1V
Ensure your load resistor is 100K, filter capacitor is between 0.1uF (100nF) and 47uF
or reduce the SetVoltage() 12.41 multiplier.
P) After step 9, nothing happened (the voltage didn't change)
Your inductor wont work try another one, or transistor Q1 isn't working right
P) Different circuit output voltage are off by a relatively constant amount
Adjust the 12.41 multiplier constant in the SetVoltage() function
P) The circuit has poor regulation, it varys by more than half a volt
Regulation needs a minimum load and filter capacitance, however at high voltages
the regulation wont work as accurately.
At high loads, the output voltage will decrease.
Check your circuit analog out (Aout) is your output voltage divided by 15.
-there might be a problem with your resistor voltage divider.
Or, try a different inductor to see if that's limiting the output.
If you rapidly change the output load, the output voltage will bounce around.
P) The circuit wont generate a voltage above 6V.
Try a different inductor, check your Q1 transistor is wired correctly, replace D1