I'm trying to create a power supply that ranges from .15 to .25 Volts at 65 to 80 micro amps. I'm using an Arduino Uno and I plan to control the circuit with a Bluetooth. Can anyone help me with this?
Thanks.
Those are some "strange" requirements... What's the application?
Creating a Variable voltage/Ampere Circuit
Voltage & current can't be controlled independently because they are related by Ohm's Law (a law of nature with man-made units-of-measure.). For example, you can make a 0.15V power supply but the current will be determined by the resistance/impedance of the load...
For example, with nothing connected (infinite resistance) you'll get zero current. With a short (zero Ohms) you'll get zero-voltage (and possibly a fried power supply!). With a "normal" constant-voltage* power supply, current depends on load. It's also possible to make a constant-current power* supply where the voltage depends on the load. (Constant current power supplies are somewhat rare except as special purpose LED power supplies.)
I'm trying to create a power supply that ranges from .15 to .25 Volts at 65 to 80 micro amps
A digital-to-analog converter (DAC) will convert a digital value to a voltage. The Uno has an ADC but no DAC so you'll have to add one, or there are ways to "fake it" with filtered PWM or you can make a resistor-ladder DAC. You'll probably need a voltage divider (2 resistors) or an active attenuator (made with an op-amp) to reduce the range down to 0.25V.
I plan to control the circuit with a Bluetooth.
Of course, you'll need a Bluetooth shield (add-on board) and you'll have to transmit/receive "numbers" representing the desired voltage. The hardest part may be the Bluetooth. I assume you'll be using a cell phone, so of course you'll have to write an application for the phone.
- A variable power supply is considered to be "constant voltage" because under normal conditions the voltage is set to a particular voltage independent of the load. The same goes for "constant current" power supplies. A dimmable constant-current LED power supply is technically a controlled- current supply but it's classified as constant-current because the current is independent of the load (under normal conditions).
DVDdoug:
Voltage & current can't be controlled independently because they are related by Ohm's Law (a law of nature with man-made units-of-measure.).
Sorry but this is not true. The relationship between voltage and current depends on the load type. A perfect resistor is linear and therefore obeys Ohm's Law. Pretty much any load involving a semiconductor will be non-linear and will not obey Ohm's Law.
Sorry but this is not true.
Yes it is read the answer again, and think what the OP is asking for.
You can not control current and voltage independently they are interrelated irrespective if the relationships is linear or not.
First off thank you everyone for the replies. I really appreciate it because I need the help.
This is clearly a case where I don't know enough to know what I don't know.
I just got a Arduino Uno kit and I'm looking for a way to build a low powered tens unit. That's the application. I got those voltage/amperage numbers from measuring the output of an actual tens unit in roughly the power output that I'm looking for.
So if anyone has any suggestions I'm all ears.
Thankyou.
The output from a tens machine is likely to be very high impedance and at at reasonably high voltage , probably pulsed.
It’s not clear how you made your measurements , but I expect they are wrong due to the output impedance .
If it were correct , building a supply to your specifications is difficult and will need a number of external components .
Think I’d do something else .
Measuring an unknown voltage source with a DC meter will just
give an average of the voltage there. You must also know if
it has an AC component and what the waveform is like.
Herb
jjajones:
...because I need the help.
This is clearly a case where I don't know enough to know what I don't know.
I just got a Arduino Uno kit and I'm looking for a way to build a low powered tens unit. That's the application.
So if anyone has any suggestions I'm all ears.
I know you probably don't want to hear this, but I suggest you shelf this project until you acquire enough knowledge and experience to not electrocute yourself, because at your apparent skill level, working with the voltage levels needed, there is a distinct possibility that will be the outcome! Running currents through your body is VERY DANGEROUS! And if you don't know what you're doing, you can easily make a lethal mistake.