Ultimate Night Vision Headlamp - 500+ lumens with only 8 watts

Step 8 Solder brightness resistors

refer to the schematic below. we'll build it using "point to point" wiring.

R1 = 680 ohm (blue gray brown)
R2 = 1200 ohm (brown red red)

these values worked for my buckpuck despite a somewhat misleading note in the datasheet, so test your resistor values before soldering.

these values give you FOUR overall power settings:

• both switches off: full power
• one switch on: 1/2 power
• other switch on: 1/4 power
• both switches on: 1/8 power



---

soldering note: these particular switches are made from fairly melty plastic so make sure you solder them rapidly. if you heat them for a long time they will melt inside and not switch properly. the best way to solder them without overheating is in 3 steps:

1) heat resistor lead and melt a small blob of solder to it ("tinning" it)
2) heat the switch lead and melt a small blob of solder to it also
3) now hold the resistor lead against the switch lead and melt the two solder blobs together, without needing to add any new solder.

this is good soldering practice in general anytime you are soldering something that is heat sensitive (such as the battery holders)

Comments

[bbennett2]

Is there a way to use 2 turquoise, and 2 red leds on this model, and then use one of the buttons to switch in between the 2 colors? I'd like a headlamp with red led's so that I do not lose my natural night vision when hiking at night; however it would also be nice to have the turquise lights for times when I want a more traditional headlamp... any suggestions?

[nutsandbolts_64]

Turquoise-colored light is still within the range of your night vision, so you don't need to switch to red.

[mrsayao]

Hey Dan, Great work, I've been meaning to pick up this project for several years now and here I am, you're truly an inspiration!! I was able to source most of the parts, the only difference is that I'm using a single 9v alkaline battery due to portability needed. How would I calculate the resistors I need? I'm using 4 green LEDs that are spec'ed similar to the cyans. I'm not using this setup for a headlamp, so I don't need the full brightness, yet I'd still like to use resistors to lower the brightness further. I purchased a buckpuck rated for 1000mA. With 4 LED's hooked up @300mA each (1200mA total), does that mean I don't need the resistors since the buckpuck will only output 1000mA max? Each LED would be receiving 1.75v @ 300mA (2v accounted for the buckpuck).... Please please correct me if I'm wrong! I have a somewhat basic understanding of all this, but I don't have a teacher to tell me otherwise! Thanks!

[Gavin.Perry]

For 9V use 3 LEDs in series (if Vf of LEDs is <3V) or 2 parallel pairs of 2 LEDs each. In general you want the power supply voltage a few volts more than the batteries. Now you can use a simple resistor to set the current. Say your forward voltage is 6.8V, at 9V in you have to drop 2.2V so for example 220mA, you need 2.2/0.22 or 10 ohms. For power it's V*I so 2.2*0.22 <0.5W use two 20 ohm 1/4W resistors in parallel if you don't have 1/2W R's, or 3 30 ohm, or 5 47 ohm etc. see below for why to use more larger Rs (small wattage).

The brightness will dim slowly as the battery power drains and the voltage drops, I consider this a good thing, rather than suddenly running out of light. For more fun (and a bit more work) you can arrange a set of switches that add in one 47-50 ohm resistor in parallel, for each switch (little DIP switches are good for this) Each switch will add in 40mA or so. Thus you can cheaply and easily adjust the brightness to the need at the time. Your eyes adjust to a huge range of brightness, often 40mA of light is all you need if you aren't trying to read and want to stay somewhat dark adapted. There is no need to have the light on "full blast" when you don't need to waste that power. And it's a lot cheaper than a IC current regulator.

Look up series and parallel if you aren't sure which is which.
I hope this helps, I love having cheap LED lights that I can adjust to the need at the time. I also do a similar trick with an LM317 wired as a current regulator, but that's another story.

[mrsayao]

Hi Gavin, thanks for the info! I studied hard and was able to complete
my project, http://www.instructables.com/id/LED-Light-Up-Sims-PlumbBob-That-green-pylon-above/ . I ended up using 3 LEDs with a buckpuck like how Dan did because of my own limited experience with electronics. He does use a LM317 in a different istable. Can you check out my istable and let me know what I can improve on? I decided on not using any switches to control the current, I bought a 1000mA buckpuck but only needed 750mA to achieve the best efficiency, so I calculated the resistor value and put some in parallel in order to get closest to 750mA. Thanks again!!

[rmccurra]

Is there a special way of measuring the current to the leds? I am getting results in the mid 300mA regardless of what resistor is used. Thanks.

[fjguilfoyle]

so far so good!!! What is the best way of soldering to the pins that stand up from the buck puck to connect the LED and switch wires? S Thanks for your help

[squirrelwithnuts]

I am also slightly confused. I didn't want to use resistors and have it on full brightness all the time and so I figured that I did not need to connect the cntl and ref pin because when the switches are off there is no connection between them but it does not work with them not connected and it also does not work when there is a wire between them. It only works when I put a resistor between them? What am I missing? Thanks.

[fjguilfoyle]

Hi Dan or anyone else who can help, I am a total beginner to this but beguiled by the potential applications and the ingenuity of the device. Resistors are not noted in the list of what is required but I assume that they are. I assume they are devices that regulate the amount of power delivered to the LEDs. Where does one get them? I assume that from the diagram that you need 2 x 1200 ohm (R2) and 1x 680 ohms (R1). In your instructions you suggest that you test the resistor value prior to use, how does one do this? I know nothing about soldering, what type of solder material is recommended for the project? Can one use Wire Glue? Thank you so much for your help. I really appreciate your wonderful work and your willingness to share it with a neophyte like me. I am very excited to see if I can actually build this and make it work. Best wishes John

[benstern]

The Buckpuck datasheet says to: "place a capacitor across the input terminals when the distance to the DC power source is greater than 18 inches." Should I do this? If so... how do I go about doing it?

[Bill H]

Dan - Can I use a 0-5000 ohm slide pot in lieu of the resistors? I have one and I'm worried about the zero ohm setting damaging the buck puck. I have all the parts and I'm getting ready to do the assembly. Thanks for the very well written instructions.

[dan]

yes, you can use a slide pot, it is just a sense resistor, no power goes through it.

[steve.filmer]

Hi Dan, The datasheet implies that full power is equivalent to 5000 ohms. They also state to divide by 50 for the % output current. Your resistor values imply that full power is equivalent to 2500 ohms. ie 1200 gives 50% Is this what you found and what you mean by the misleading note in the datasheet. I am building mine with resistors in series and having switch in parallel with each resistor. This gives you 0, low medium and high power; or should when I get the resistance values sorted out.

[dan]

i found the datasheet to be inaccurate about how to calculate the current based on resistor values. actual current seemed to be non-linear function of resistor value.

[turgan]

Hi Dan, a beginners question: when you say "these values worked for my buckpuck despite a somewhat misleading note in the datasheet" do you mean other resistor values wouldn't work at all? I have 1Kohm and 470ohm's. Would these be ok, except that the lamps will be a little brighter?

[turgan]

1Kohm and 470ohm did work great, thank you for this instructable.

[Pacca]

hi dan! wat is the pin-size hole for? because the 3021-D-E-1000 model doesn't have it. didn't change anything? thx

[dan]

what pin-size hole? if you mean the adjuster dial (which is about 6mm diameter hole), i've updated the comment in the photo regarding that. if you dont have the dial, no problem. as for pin-size holes, i dont think there should be any of those, if you have a pin-hole i'd cover it with glue.

[claytor1999]

Dan - how do you "crank it to 11". Do I have to dig into the buckpuck to do that? I notice there's a small pin-size hole on the same side you're showing - but it's in a different position. Thanks - the light works great.

[dan]

just turn it all the way clockwise, gently.