Intro: LM317 Portable Voltage Regulator
First Instructable for me. I've been wanting to build an adjustable voltage regulator in an Altoids tin for quite some time. A variable voltage of between 1.2 & 6volts for testing small dc motors and LEDs retrieved from old electronics would satisfy my needs.Googling the net for project designs surprisingly didn't produce any results. I thought "See a need, Fill a need!" & thus began this project. I've been tinkering in electronics for only a few years now. I don't pretend to know much & appreciate any & all mistakes being brought to light so they can hopefully be corrected.
With a DMM attached to the output posts to accurately set the voltage one could also power an Arduino or other small project. Using a 9 volt dc battery connected to a 2.1mm barrel jack it's small enough to fit in yer pocket & so totally portable.
I consider this a fairly simple & fun project leading to a totally useful & versatile tool when complete. Soldering on the breadboard pcb is a bit challenging but a decent iron with small tip makes short work of it.
With 9 volts dc provided by wallwart or battery a project can be supplied with between 1.25 - 8 volts dc by connecting to 2 posts with alligator clips or bare wire. A toggle is included for on/off with an led to show when powered up and a knurled knob for voltage adjustment. All electrical wiring & components safely contained within an Altoids tin.
After making who knows how many drawings attempting to fit this circuit into the tin I found putting it down on graph paper allowed me to see where everything goes quite readily. I've just drawn enuf to get the gist of it. It is a regular breadboard after all with double power rails top & bottom (tho I have only used the negative rail) & 2 solid rows of 5 holes high each.
Is Texas Instruments datasheet. You'll find an almost identical schematic when googling Nat Semiconductor, Fairchild, et al. This is the basis of my design. Please note the R1 resistor here is 240 ohm, I've replaced it with a 470 ohm for a reason I've now forgotten but I do remember reading somewhere this value should be 100 - 500 ohm.
The 3rd image is a page of my design notes showing the late stages of how I arrived at this particular configuration. I've actually been working on this for over a year, off & on, with the project only coming together during this past month.
I struggled with trying to move my completed project, which btw I credit afrotechmod on uTube for giving me an understanding of how to make an adjustable voltage regulator using the LM317, from breadboard to a circuit board which would fit in an Altoids tin. I settled on a breadboard pcb, which really simplified the whole process. These can be had for 3 bucks from Pixel Print in Vancouver, BC, using only half a board for this project, cost $1.50, which is most reasonable.
breadboard pcb (cut in half)
0.1uF ceramic cap
1.0uF elec cap
330ohm resistor (for led)
5k potentiometer & knob
3mm led green (or red, or amber,etc)
2.1mm barrel jack adapter
2 x posts for output power
wires of various lengths 22 - 24AWG
heat shrink tubing (for exposed connections)
Altoids or similar sized tin
wall wart 9 volts dc with 2.1mm barrel jack
hot glue gun
brad point drill bits
files or sandpaper
dremel with sanding drum to enlarge/shift holes
I found brad point drill bits, although for wood, do an excellent job cutting through the soft tin of the Altoids container. Becauase of the side cutters on the bitface the hole made comes out perfect without a lot of fuss & bother using just a hand held drill. see hole in side of tin in drillbit image.
When drilling holes in top of tin I find it best to use a block of wood to support the tin while applying pressure so the metal doesn't warp. The two larger holes were drilled with a normal drillbit, hence the flat-sided circles. Washers when fastening components to the lid will hide these irregularities. The smaller holes were drilled with a bradpoint and thus are clean & round.
To begin start by cutting the circuit board in half & filing the corners roundish to fit the curved corners of the tin. Next mount the barrel jack adapter. The holes in the circuit board are too small to accomodate the leads on the bottom of the adapter & have to be reamed out a tad bigger. Dremmeling the adapter leads down in size doesn't hurt either. Solder in position then place a piece of acetate or other thin material beneath to insulate the solder joints from shorting out on the tin. Probably a good time to position the hole for the barrel jack on the front of the tin, keeping the hole beneath the lip of the lid.
The 2 caps, 2 resistors and any wires needed on the board can be soldered in place now. I used solid core here & stranded wire for all the wires that need to flex when the tin is opened & closed.
Next is to position the components on the lid & drill the holes, keeping in mind room has to be left on the underside of the lid for the hinged lip at the back of the tin. I found holding parts with helping hands when soldering the pre-measured wires onto them works well. A 6" (or metric) ruler is handy to roughly guesstimate the length of wire needed. The LM317 is hot glued directly to the tin lid, relying on the tin to dissipate the heat generated.
I believe in repurposing electronics so you might have noticed almost all parts used here have come from other electronics, or in the case of the container, from numnums! I do test all parts with a digital multimeter before soldering in place. As far as cost for this project I'm sure a lot, if not all, these parts can be found in your parts bins. Personally, I bought the Altoids - 2.20, circuit board - 1.50, toggle - 0.50, green led - .20, & the green solid core wire - maybe a few cents. Under 5 bucks - not bad!
I find a clean, well-lit workspace to be ideal. Wish it would just stay that way!
With the 5k potentiometer, soldering the far left pin (when looking at the underside of the lid in the pic) to power and the middle pin to ground gives you clockwise rotation when increasing the voltage. Soldering to the pin on the right (in pic) would provide counter clockwise rotation.
Once the opposite ends of the wires are soldered in place on the circuit board it's time to slowly squeeeeze the lid down, pushing wires this way & that so everything fits comfortably.
When first powered up the DMM should give a reading of 1.25 volts minimum.
Using a 9 volt wall wart gives a minimum 1.25 & a maximum voltage of 8.11 & all points in between. Marking the positive/negative with a sharpie next to the output posts should complete this project. Which reminds me, I chose this style of power post as I plan to be attaching alligator clips & appreciate the spacing & ruggedness. Small holes in the tops of the posts allow bare wire in for quick connections. Depending on ones needs the posts can easily be changed for whatever suits the purpose. Which can really be said about almost any part of this design. Stripboard or whatever can be used instead of the breadboard pcb, the led colour & size, the toggle, the potentiometer, your choice! Go for it!
Hope you enjoyed & it will be a pleasure to hear your comments! Be safe & re use, re purpose when possible.
Finalist in the
Pocket Sized Contest