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So I want to make a variable power supply and this is one of my first (sort of) hard circuit. And I figured that throughout my project making, I will need a power supply but sadly it costs too much. I tried to salvage as much as I can until I encountered these variable resistor-looking volume knobs. Can they be of any use?
can volume knobs can be used as potentiometers?
- Thread starter ZetaOjoy
- Start date
I am not quite sure about you are trying to do but if you are planning to do a variable power supply by simply using a potentiometer you are on the wrong way.
On the other hand, if your question is if a fader (longitudinal pot) is the same as a rotary potentiometer, yes, electronically are the same the only change is the way they mechanically operates. Then, there are values and, not less important, linear or logarithmic behaviour. To do a quick description, linear increases, lets say, in the same amount per mm, and logarithmic increases (or decreases) in a weird manner, being very low variable in most of its run and a lot of change in a narrow part of it. This depends on the use you pretend.
Of course, if you want to use as regulation part of a variable power supply my choice would always be linear pot. but, again, to do this you require some more components and the best choice is to use an IC, like the well known LM317
On the other hand, if your question is if a fader (longitudinal pot) is the same as a rotary potentiometer, yes, electronically are the same the only change is the way they mechanically operates. Then, there are values and, not less important, linear or logarithmic behaviour. To do a quick description, linear increases, lets say, in the same amount per mm, and logarithmic increases (or decreases) in a weird manner, being very low variable in most of its run and a lot of change in a narrow part of it. This depends on the use you pretend.
Of course, if you want to use as regulation part of a variable power supply my choice would always be linear pot. but, again, to do this you require some more components and the best choice is to use an IC, like the well known LM317
smooth_jamie
- Joined Jan 4, 2017
- 107
Hi ZO,
A variable power supply is a great first project, a variable lab power supply in my oppinion is a must! You can't often build a DIY unit cheaper than what you can buy from China, but if you're able to source any salvaged parts Rod Elliot (ESP) has a decent schematic on how to build one: http://sound.whsites.net/project44.htm.
If you can save up some money, buying a limiting power supply is probably better in the long run. My first was the Lavolta BPS305 from ebay which cost me £55 delivered from China, it still works great to this day and I'd recommend it if you're just building up your kit.
You can also buy current/voltage limiting modules for as little as £20, or if you are really really pinching pennies then you can always just buy a buck-boost DC-DC module for £1 delivered, but I'd recommend something with limiting/protection built in (worthwhile in the long run).
Additional:
It need not be said, but you will of course need more than just a potentiometer to make your variable power supply.
A variable power supply is a great first project, a variable lab power supply in my oppinion is a must! You can't often build a DIY unit cheaper than what you can buy from China, but if you're able to source any salvaged parts Rod Elliot (ESP) has a decent schematic on how to build one: http://sound.whsites.net/project44.htm.
If you can save up some money, buying a limiting power supply is probably better in the long run. My first was the Lavolta BPS305 from ebay which cost me £55 delivered from China, it still works great to this day and I'd recommend it if you're just building up your kit.
You can also buy current/voltage limiting modules for as little as £20, or if you are really really pinching pennies then you can always just buy a buck-boost DC-DC module for £1 delivered, but I'd recommend something with limiting/protection built in (worthwhile in the long run).
Additional:
It need not be said, but you will of course need more than just a potentiometer to make your variable power supply.
Yes, you can use a volume control as a potentiometer, so long as you know and understand the limitations.
If you think that you can take the output of the power supply and then reduce the voltage with a potentiometer (as a voltage divider) you are making a mistake. With any appreciable current output, the potentiometer will burn out. As stated in post #3, you need to use the pot to control a voltage in the the voltage regulation circuit using other active components such as voltage regulator chip.
Volume controls come in two resistance characteristics, linear taper and logarithmic taper. You can use either to adjust a current, voltage, or resistance, so long as you understand the difference between linear and log taper. To check whether your pot is linear or log taper, set the control to the middle position. Measure the resistance between the wiper (or slider) contact and each of the outer contacts. If the resistances measured are almost the same (within 20%) then it is linear taper. If the resistances are vastly different then it is log taper.
Pots used as volume controls are generally log taper.
If you think that you can take the output of the power supply and then reduce the voltage with a potentiometer (as a voltage divider) you are making a mistake. With any appreciable current output, the potentiometer will burn out. As stated in post #3, you need to use the pot to control a voltage in the the voltage regulation circuit using other active components such as voltage regulator chip.
Volume controls come in two resistance characteristics, linear taper and logarithmic taper. You can use either to adjust a current, voltage, or resistance, so long as you understand the difference between linear and log taper. To check whether your pot is linear or log taper, set the control to the middle position. Measure the resistance between the wiper (or slider) contact and each of the outer contacts. If the resistances measured are almost the same (within 20%) then it is linear taper. If the resistances are vastly different then it is log taper.
Pots used as volume controls are generally log taper.
What are the old savaged parts you've collected so far?
Is there a big enough power transformer for your project?
A BJT either PNP or NPN as a pass transistor, if better do you have a LM317 IC ?
Some big electrolytic capacitors preferably 1000uF, 100uF and 47uF and 10uF...
Some smaller transistors like BC547, 2n2222, or C945 etc
With your list of parts, may be we can figure out or design a simple 3 or 4 transistors variable power supply for you..
The power supply I am using now is one I made many years ago. It used a LM723 chip that controls the 2N3055 TO3 transistor with a volume control.
Allen
