Introduction: Mini Adjustable Voltage Regulator

Picture of Mini Adjustable Voltage Regulator

The goal was to make a variable power supply and make it as compact as possible. This is what I made. I know there are many other voltage regulator projects out there, but I wanted to make mine to suit my needs. This instructable assumes you know how to solder and basic knowledge of how to align circuit components in a tight configuration. Let me know if you have questions, or try for help also.

The items listed below are what I used, or something similar. It isn't necessary to use exactly the same components that I have used, but I am giving you a few links that might help. I also didn't use the capacitors like shown, because I only use it to power things temporarily, and typically don't care if there is some fluctuation.

Bill of Materials

  • Dual 9v battery terminal (this one is parallel connected, I need series connected, just to get higher voltage range, but if you only need up to 9v, then this would work. If you can't find a series connected version, you can easily modify this one to be series)
  • If you use battery terminals like I've shown, you will need some prototype board, similar to this, but I highly recommend buying the dual terminals above because it created more work to solder them properly:

  • Mini Digital Volt Meter
  • A potentiometer with a knob, the LM350 recommends R2 = 5kohm along with the R1 = 240ohm, but I used R2 = 1000ohm and R1 was a 10-turn 20kohm pot (If I ever rebuild this, I would definitely look for a physically smaller one, but still 10-turn, however this is what I had on hand). I show other potentiometers, but those were very high values like 500kohm and 2Mohm, they might have worked, I just chose not to use them.
  • 1000ohm resistor (if you use a 20kohm pot)
  • LM350 3A Voltage Regulator
  • Toggle Switch something like this is what I used:

  • Small alligator clips
  • Some wire
  • Solder
  • Heat shrink
  • Duct tape or something to apply to the back of the volt meter as insulation (short circuits are usually bad)
  • Epoxy (I used 5 minute type, but others could be used)

Note: If you use the dual battery terminal listed, then you would not need the PCB

Step 1: Schematic and Battery Terminal Prep

Picture of Schematic and Battery Terminal Prep

For the circuit, be sure you check the datasheet of whatever voltage regulator you are using. I chose the LM350 because it has higher current output, but I've used LM317 in the past. If you plan to drive something with higher current needs, you might need a heat sink.

You will need to cut wires and cut open the plastic sheath around each battery terminal, if you use the individual 9v battery terminal with wires. If I were to build this again, I would use the dual terminal type on the first page, and modify it to be series rather than parallel like that link shows.

Then you need to cut the prototype board to fit roughly the size of the two batteries together.

Solder the terminals onto the prototype board as shown, and add a short wire beneath the terminals on one end (as shown the red wire in the 4th picture). This will put the batteries in series to give 18v, when you connect the other terminals. Keep track of which is + and - for correct operation.

Step 2: Voltage Regulator Placement and Wiring to Voltmeter and Potentiometer

Picture of Voltage Regulator Placement and Wiring to Voltmeter and Potentiometer

I placed the voltage regulator on one edge so that I could bend the input terminal and make it stick through to the positive battery terminal. Then you just bend it to touch the terminal from the other side and heat it up and apply solder.

Then you cut the resistor shorter and bend one end around so it can be soldered to the regulator terminals as shown. I planned ahead and applied heat shrink tubing once I had the wires soldered, but don't do it too soon unless you know where to make the next connections.

Refer to the schematic to understand where the volt meter needs to be connected. The red wire is the power for the meter itself, so I connected it to the 18v, and the black wire to the ground point which will be after the switch.

I think I missed taking a few pictures for the rest of the wiring, but if you follow the schematic, you will see the battery ground is connected to one terminal of the switch, then another wire will connect to a terminal of the potentiometer (see yellow arrows on 6th picture).

Then the adjust terminal of the regulator will have a wire soldered to it which will go to the one terminal on the potentiometer. And the third terminal on the potentiometer is unused. Be sure you check that you have adjustable resistance. If you connect the two on the "ends" of the potentiometer, it will just be the max resistance and not on the wiper. The potentiometer I used had its own schematic showing what each pin 1, 2, and 3 are.

The voltmeter black ground will connect to the same terminal of the switch that the potentiometer is, and the red positive wire will connect to the bent terminal of the regulator, which is the Input voltage. The white wire will connect to the Output of the regulator. I made each wire length fit to the distance and location of each connection, keeping enough slack to allow easy assembly.

Be sure you add duct tape or something as an insulator on the bottom of the voltmeter.

Step 3: Final Assembly and Epoxy

Picture of Final Assembly and Epoxy

At this point, all the wires should be soldered. You can carefully attach the batteries and turn on the switch and measure the voltage from the Output to the Ground terminals and turn the potentiometer, the voltmeter reading should change.

If it makes it easier, solder some wire (see the silver wire) to the Ground terminal of the potentiometer and the other wire (copper) to the output of the voltage regulator and solder the wire to the alligator clips (you might need to redo the heat shrink if you already did that earlier.

If this test was OK, then you can move on to epoxying everything together. No secret or best method, just hold the pieces where you want them to be, then find some way of temporarily holding them together. I used Scotch tape and a Quick-Grip clamp or something, then applied some 5-minute epoxy with a toothpick and just waited until it was dry, then rotate the assembly and add more epoxy as needed to ensure it holds tight. Then remove the tape, clamp, or whatever temporary holding method you used.

Step 4: Short Video Showing Voltage Changing

Picture of Short Video Showing Voltage Changing

The minimum output is based on the voltage regulator's internal reference voltage (look at the datasheet formula), and the maximum output is based on the batteries connected and how much energy they have left (as well as the maximum specified in the datasheet, in case you connected much higher voltage).

Hope you enjoy making this.

Step 5: Example Usage

Picture of Example Usage

Just showing an example of how I use this adjustable power supply. Here I have a small humidity sensor and another volt meter display to read its output. I set my main unit at 5.0v and the sensor is reading 1.8v. By the datasheet, that means about 40% RH. This made it easy for me to do a quick check of multiple locations, without needing to build a permanent circuit. Eventually, I will just build a permanent circuit or buy a small unit to display the current humidity.


cfreitas (author)2016-08-17

Hi ! Sorry for bring this up again, I hope this will not be a problem....
I bought everythng to make this Instructable, I really need something like this for my lil lab... btw, i´m a begginer, and I only found this Mini Digital Volt Meter I atached the images. The seller told its 3.5 / 100 Volts, and the white cable can work with voltages as small as 1.5 volts. Do you think I can use it ? ( was very cheap anyway ) Thanks in advance !

MagicTK (author)cfreitas2016-08-17

No worries. It's good to get questions like this because sometimes other people have the same question. Do you have a link to this volt meter? I can tell more by the description and specs.

The one I posted in the link above requires 4.5v to 28v DC input, then it can measure 0v to 99v DC.

Power specifications:

  • 4.5V to 28V DC power
  • 0V to 99.9V DC measurement
  • MagicTK (author)MagicTK2016-08-22

    You're on the right track. This is similar to the one I have listed above, except it measures 2.5v - 30v, which is sufficient for most applications like this little power supply. The ones I have actually measure up to 100v DC, but you will be perfectly OK with this one below.

    And yes, you could use a mini ATX power source as the input to the voltage regulator, in place of the two 9v batteries in series like I show. You will just be limited to the max voltage the ATX power source output is. Most are 5v and 12v. Sometimes have 24v output. I would recommend the 12v or 24v, but you can use any voltage up to the max input voltage of the regulator IC that you choose. If you are going to run a lot of current through it, I would recommend using a heatsink on the regulator. You could even screw it to the ATX case. The advantage of this circuit is the fine-tuning you get with a 10-turn potentiometer. Attach pics whenever you build yours.

    cfreitas (author)MagicTK2016-08-22

    The only link I found for this Volt Meter is this one :

    cfreitas (author)MagicTK2016-08-18

    Thankyou ! I will try to find a link. here in Brazil there are no much info about this type of component, they sell it and "thankyou for your business !"... By the way, would be perfect for me if I can use this with a PC Mini ATX power source. Do you think is safe ? Thankyou for your response !!!

    cfreitas (author)cfreitas2016-08-17

    Well I think its exactly the same :)

    MagicTK (author)2016-05-26

    There are many calculators out there to help determine the fixed values (if you wanted to used fixed rather than potentiometer), however, this link has a nice table that shows various ranges. I have not had any issues with using the 20K and 1000ohm as noted. If you were to use a 10k, I think you would be OK with 500ohm. Try out the calculator and figure out what voltage range you will be working with, that might help determine what values make most sense. Also, it's a simple formula, try doing a few manual calculations just for fun.

    Cjmayer29 (author)2016-05-26

    Oh sorry. One more thing. Im guessing that if you use a 1000 ohm resistor with the 20k pot, If i use a 10k pot i would use a 500 ohm resistor. Correct? Or am i doing this wrong?

    Cjmayer29 (author)2016-05-26

    Thanks! Helps alot! Theres just so many different alterations and options its hard to tell what to get! Love the instructable too, its exactly what i was looking for!

    Cjmayer29 (author)2016-05-24

    Can you put a link to the potentiometer you used please? Im having trouble finding the right one

    MagicTK (author)Cjmayer292016-05-25


    You can buy them on Amazon for about $14.00 each

    Or I found some on eBay for much less, around $2.95 each different brand, but they still function the same.



    fr3dd4 (author)2016-01-05

    This is a project is a great idea and I may try it soon. Although I have a question on creating a voltage regulator with an input about 20mV. With that low of an input I found a way to have an output of 5volts. The problem is when connecting to a charge a device, the output voltage drops more than half. Is there a way to regulate the output if I am unable to increase my input?

    MagicTK (author)fr3dd42016-02-02

    Hi, thanks for your question. Sorry it took so long for me to reply. I'm not 100% sure what you mean by you found a way to have a low input (like 20mV) and output of 5v.

    V = I * R <--- This is still true

    So if you have a 10ohm load as an example, with a voltage of 20mV , that gives a current of 0.020V / 10ohm = 0.2mA

    At 5V output, that gives a current of 5V / 10ohm = 50mA

    These are just example calculations. If you have a "fixed" load, such as a charge device, chances are, you will need more than just 20mV as an input.

    This link is for a Joule Thief which shows how to step up a voltage from low to higher, but I don't think it will step up 20mV and still have enough current to power a charging device.

    If someone has better method to show the calculations, please do so.

    Dokramuh (author)2015-11-29

    Hi, this was a very interesting instructable, but I have a couple of questions that I hope you could answer me. Not really having much knowledge on electronics, is there a way to have a switch or button to reset the voltage back to 0? Also, can you make it so the voltage goes up slower? Thank you very much, and I'm really hoping to build this.

    MagicTK (author)Dokramuh2015-11-29

    Hi, thanks for the questions. I enjoy helping answer anything that I can.

    To make it switch back to 0v every time, you would need to add more circuitry with something like a programmable resistor to change the value of R2 to whatever value is needed to make 0v output by default. I just remember to turn ON the power switch, then check the voltage prior to connecting it to anything. There might be some other programmable power IC's, but I've never tried looking.

    An alternative would be one of these on this page (just look for adjustable output): <-- 4-12v with about 2A output <-- 9-30v with about 2A output <-- 2-12v with about 300mA output

    So it all depends on what output you might need. The LM350 can give you from 1.2v - 30v at 3A of current (heatsink might be required).

    With my design, the voltage goes up as fast as you turn the potentiometer. If you have a 1-turn pot, it is difficult to control the voltage rise rate. The 10-turn gives very fine, smooth adjustment.

    With a programmable, I am not sure exactly the setup you would need to make it 0v start and slow rise. Maybe any programmable IC (Raspberry Pi, PIC, Basic Stamp, etc...) could be incorporated.

    Good luck, and post your project (or at least a link) in here when you are finished.

    Dokramuh (author)MagicTK2015-11-30

    Thanks so much for the quick response!

    I'm trying to pull off a Fallout 4 cosplay, and the idea is to have a functional Laser musket, which is a laser rifle operated by a crank, in which the more you crank it the more power it has. (see video below). Another idea I've had is to have a voltage controlled switch that will turn the circuit on when voltage is higher than x, and turn it off when it's lower than x, basically turning it off by cranking it in reverse.

    This is all working on the premise that CCFL and LED lights can be dimmed by adjusting the voltage. I hope I can pull this off, it's a bit ambitious for my first circuit outside of what school taught me!

    AJackOfAllTrades made it! (author)2015-02-01

    While I didn't make the exact same device you did, I used your instructable as research to help me size the resistors to build an adjustable voltage regulator prototype for an adjustable 12VDC ATX power supply mod that I am doing. I had the 10K pot, the LM317, and the 1K Resistor on hand. Nice clean adjustment from 1.2VDC to 10.7VDC. Just giving credit where credit is due. Thanks!

    MagicTK (author)AJackOfAllTrades2015-11-29

    Very cool. I always enjoy hearing of similar projects or being-inspired-by type of projects. I have a really nice PWM circuit which was from a computer case fan controller design I found online. It can give true 0% - 100% duty cycle. I also made it with an adjustable frequency. I like using the 10-turn pots like the one shown in the pictures above. It provides very fine control. I happened to find some on ebay that are much cheaper than the one I used here, in case you ever want to find them.

    T0XICMASS (author)2014-12-04

    What are the odds that this could be used on a Nixie clock so I don't kill myself if something short in the clock's circuits and stuff,or would the power it draws not be able to be handled by this reg?

    MagicTK (author)T0XICMASS2014-12-05

    If I understand you correctly, you want to use this to power a Nixie clock? Like this:

    or do you want to use the Nixie as the digital display instead of this volt meter I show?

    It should work to power a clock. Not sure why you would want to use an adjustable power supply like this, rather than a fixed voltage regulator circuit, but the current draw is low, but would not last too long if the display was ON continuously.

    • Clock works from 7.5 to 15V DC, but 9v or 12V supply is recommended choice
    • Power consumption:
      1.9W (215mA@9V) from wall plug power supply (all 4 digits to display)
      2.3mW (0.75mA@3V) from backup battery ( 3V Panasonic CR2330).
    Metalman000 (author)2014-11-05

    hi, great 'ible! what do you use this for?

    MagicTK (author)Metalman0002014-11-05

    Thanks. I'm glad you like it.

    I use it to provide power for simple parts like light bulbs, LEDs, sensors, control units for basic
    function check, circuits on a breadboard when I need it to be portable
    and not rely on a large plug in power supply. My intent is for
    temporary use, not permanent. For permanent, I would just design a
    power supply circuit to be a fixed voltage and attach it to the device.

    MagicTK (author)2014-10-29
    MagicTK (author)2014-10-29

    If I were to build this again, I would use something like these mini banana plugs and jacks for instead of just soldering the alligator clip leads directly to the potentiometer's ground point and the voltage regulator's output. I did this on a previous design, but it was the large banana plugs. The mini would help keep the size minimal.

    Mini Banana Jacks

    Mini Banana Plugs

    MagicTK (author)2014-10-23

    Just in case anyone was wanting to try
    the series parallel switching that Lee suggested, here is one way to
    achieve it. It will switch from serial connection to parallel

    And another link about series, serial, parallel...

    MagicTK (author)2014-10-23

    Both are mostly correct... Parallel vs Series and Parallel vs Serial arrangement.

    main point was that if you have 12v input, you don't have 12v output
    for very long, but if you have 18v input, and use a regulator at 12v,
    you will have a good continuous 12v output until the 18v configuration
    is drained to the 13.25-ish range. More useful hours. This is just an

    And if you aren't drawing full current, then it doesn't matter so much.

    Jamebonds1 (author)2014-10-21

    It is nice project for basic power supply! :) Keep in mind. If you put battery in serial will lossing it current. EX: If it is in serial 9V(150mA) + 9V(150mA) = 18V(70mA) If it is in parellel, 9V(150mA) + 9V(150mA) = 9V(300mA). I would have recommend a AA to D battery.

    Lee Wilkerson (author)Jamebonds12014-10-22

    You don't lose current by putting batteries in series.

    IanPerkins (author)Lee Wilkerson2014-10-23

    You actually do lose current by placing batteries in series due to ESR (effective series resistance). But as long as its not TONS of batteries its pretty negligible ;no where near what jamebonds is eluding to. he has it all wrong. 1st clue, he called it serial lol.

    Jamebonds1 (author)IanPerkins2014-10-23

    Don't false accused me. Read all of comment first before you post.

    DabeAltis (author)Jamebonds12014-10-21

    Placing the batteries in series does not reduce current capacity.

    IE: 9V X 150mA = 1.35 Watts X 2 = 2.7 Watts

    18V X 150mA = 2.7 Watts

    9V X 300mA = 2.7 Watts

    elkaddalek (author)2014-10-23
    Lee Wilkerson (author)2014-10-22

    One other thing I just remembered: if you increase your input voltage, there will be an associated increase in heat dissipation from the regulator.

    For example, you have 9v. into the regulator and your regulated output voltage is 5v. Voltage drop across the regulator is 4v. With 18v. supplied, the regulator's voltage drop becomes 14v. Current remains the same, therefore you now have increased the power dissipated by the regulator to 3.5 times the original.

    With one switch, you could switch from series batteries to parallel batteries and only use 18v. to supply greater output voltages (12v. for example).

    MagicTK (author)Lee Wilkerson2014-10-22

    You are right, although even when I need 5v, typically my current draw is very low, so total power dissipated is nothing for me to worry about.

    I do like the idea of using a switch, like a DPDT to change the battery connection. I have another project which I actually did that so I could provide 6v or 12v to a motor for low and high speed using lantern batteries, but the exact same thing could apply here. Nice thinking.

    MagicTK (author)2014-10-20

    Thanks. My first one, I had a SPDT switch and used a 7805 and 7812 for 5v and 12v but they were just fixed voltages. I wanted adjustable, and even had a separate box to do that, but it still didn't make me happy because I always had to get my separate voltmeter to measure the output. So I added the voltmeter display. And other than the monstrous potentiometer (comparatively) it's a very compact design.

    ac-dc (author)MagicTK2014-10-21

    LM7805 and 7812 aren't really/necessarily fixed voltage. I mean that they are the same as LM350 and others to the extent that if you vary the resistance to ground with a voltage divider (pair of resistors or one being a potentiometer as shown) subcircuit (just like with the other linears) you can adjust the output voltage.

    Lee Wilkerson (author)ac-dc2014-10-22

    I've done this many times, too.

    Lee Wilkerson (author)2014-10-22

    The beautiful thing about Alkaline batteries is that you can recharge them numerous times.

    Lee Wilkerson (author)2014-10-22

    Nice 'able. I've built many voltage regulator circuits (many of them using LM-series regulators.

    One suggestion: you could sink a lot more heat away from the regulator using a small aluminum heat sink (or even an aluminum plate). 10 degrees C. collector junction temperature increase = 1/2 transistor life.

    ~/Lee the Geek

    MagicTK (author)2014-10-21

    ac-dc, thanks for your comments. While I do understand and appreciate the fact that you can buy something cheaper online (I use ), that wasn't the point of posting my build. Sometimes I think it is more fun to build something than just buy it. I think many other people feel the same, as is apparent throughout this website. Also, you are correct about the 7805/12 being variable with resistor and potentiometer, however those are at a fixed maximum of 5v and 12v (unless you know of some new method of applying them, please share by a circuit diagram). My design can go up to the max of whatever your input voltage, in this case 35v, however, I used two 9v in series for 18v, but that's what I wanted to do.

    And thanks to the other contributors for your comments.

    Of course you could use any other variation of batteries AAA to D and more. References I am finding show 9v alkaline "rated" as 500mAh as one example, except Radio Shacks site shows 150mAh. Also useful information is this comparison test

    is a better way of showing discharge rates.

    My usage is not as a permanent power supply, but rather as a temporary let-me-see-if-some-device-works type of power supply. Typically I only have it on for a minute or two unless I know something has a very low current draw.

    So, I see V still equals IR and P still equals IV. One reason I use the 9v's in series is to give me 18v input (I don't care about the mAh or total life at this point), it also makes for a relatively compact design with the 9v's. D's or other configurations would definitely work, it just means bulkier final package, which wasn't my goal.

    My main usage is around 5v and 12v to 13v, so even if I have something that draws 1A, it will last for as long as it takes for the 18v to drain down to roughly 14v (minus the internal reference voltage of the regulator) to give 13v continuous output during that entire time. Or... smaller current draw loads would just last longer.

    Helpful calculator to see rough usage times (of course it depends on the discharge curve for each battery type, see the powerstream link above)

    rickhaigh (author)2014-10-21

    Actually when the batteries are connected in series the voltage will double, and the current will remain the same. You are correct about the current doubling in the parallel configuration.

    serial: 9V(150mA) + 9V(150mA) = 18V(150mA)

    parallel: 9V(150mA) + 9V(150mA) = 9V(300mA)

    Jamebonds1 (author)2014-10-21

    Oops. My bad. mA turn out to be discharged. That would be mAH. But.... I should have say that 9V have very bad discharging at 150 mA.

    PS: This is not what your comment appear to be, due to confused writen about your parallel?

    DabeAltis (author)Jamebonds12014-10-21


    It's true that a higher discharge rate will typically reduce the Milliamp-Hour capacity of your batteries.

    DabeAltis (author)2014-10-21

    Sorry, I didn't mean to repeat what you had already replied to. Your reply wasn't showing in my browser till after I posted. You might want to edit your post to reflect 9V(300mA) on the second example.

    Victor Does (author)2014-10-21

    This is really useful! Where going to buy a couple. but now thanks to you I can make them instead! Thanks

    ac-dc (author)Victor Does2014-10-21

    Keep in mind that once you factor for the time and expense of buying the individual components, plus gas to drive to get them or shipping, it actually ends up cheaper to just buy one ready made off eBay if you can wait a few weeks for it to ship from Hong Kong or another oriental address.

    Victor Does (author)ac-dc2014-10-21

    Usually get my things from Aliexpress. But this seems to be things I already have at home :) But thanks for the tip!

    techlv (author)2014-10-21

    Remember, the higher the voltage drop between input and output, more heat will be dissipated in the LM350. A heat sink may be needed in that case.

    ac-dc (author)techlv2014-10-21

    Indeed. Voltage drop x current = watts. If it is approaching 1W or more there should be a heatsink on it.

    3366carlos (author)2014-10-20

    Thanks, I really like those voltmeters and plan to buy a few. btw, your movie doesn't work. thanks.

    About This Instructable




    Bio: Electrical Engineer
    More by MagicTK:Cabinet Door Roller for Smooth Operation and to Protect the PanelHot Pepper Powder MixMini Adjustable Voltage Regulator
    Add instructable to: