Intro: Adjustable USB Microscope
So this Lazy Old Geek is getting OLD and my eyes aren’t what they used to be. So I bought one of these USB microscopes from ebay (See picture) to see if it would help with closeup work.
Well, it sort of works. It’s pretty cheap so I didn’t expect a lot. There’s a silver wheel that’s marked as power adjustment, i.e., 25x to 200x but it seems to me it’s mostly just focus. There’s also that little plastic stand that is somewhat adjustable. I screwed the base to a piece of particle board. But it was very hard to use. I often put it on books or something but you always had to mess with the focus and it was pretty hard.
So I decided to make an adjustable motorized microscope.
Instructable Reader: Warning, this is not a project you can duplicate precisely (nor would you want to). I used a lot of parts from my scrap pile and designed and developed as it progressed. This is not a very good way to create a project and it shows. But it does work.
Step 1: Basic Design:
Basic Design: My original theory was to make the microscope position adjustable (up and down) with a motor and have another motor to adjust the focus.
I was thinking of driving the focus with a hard rubber wheel but after playing with my microscope I decided that wouldn’t work. The other option would be to take the microscope apart and study the mechanism. Well, my mechanical skills aren’t that good and I didn’t see any easy way to take it apart so decided to leave the focus manual.
For the position adjustment, I put on my ‘MacGyver hat’ and went through some of my scrap piles. I decided on using a threaded shaft to position the microscope and I have several ‘hardened’ steel shafts from printers so would use a couple as guides.
Problem: My first concern was how to hold the round microscope.
Solution: I took a cue from the existing mount and cut a half round in a piece of plastic. The microscope has a notch in it that holds it in place. (See pictures)
Problem: My major concern was how was I going to keep the threaded shaft and two guide shafts perfectly straight and perpendicular so that it would move up and down, with my terrible mechanical skills.
My ‘Clever’ Solution: From particle board, I cut the base and the top so that they were pretty square and the same length. Then I cut a piece of plastic for the moving microscope holder. I clamped all three together and drilled a couple of holes for some bolts, then bolted all three together. Now, I could drill all three at the same time so they holes would line up. And since I had a drill press, the holes should be perpendicular. (See pictures)
If I was really clever, I would have figured out a motor mounting scheme before drilling and maybe added another piece of plastic to the stack. Alas, I didn’t plan that far ahead. I am OLD you remember!
Step 2: Assembling the Frame
The first picture shows some of the frame parts. The back is missing and I took this picture before I drilled the holes from the last Step.
I used the shafts and threaded rod to help keep everything aligned. Then glued the top and bottom to the back. I used some gorilla glue, then wood glue. (See picture). Overall height is about 9 inches. Notice I used a couple of nuts on the threaded shaft to help keep the separation where I wanted it.
Next I glued the sides. I put some duct tape over the joints so the glue didn’t get all over everything.
You may notice that the sides don’t match up with the top. This was not by design. I cut them about the same size but didn’t consider what would be glued to what. I told you I’m OLD and don’t have much mechanical skills.
Step 3: More Mechanical Stuff
Problem: The plastic microscope plate needs ¼ 20 threads to ride up and down the threaded shaft.
Solution: So I used this method before. Drill the hole so that it’s slightly smaller than the diameter of a ¼ 20 nut. Place the nut underneath. Thread a ¼ 20 bolt with another nut and put a big washer on it. Thread the bolt through the plastic into the nut. Tighten the top nut so that it pulls the bottom nut into the plastic.
Well, I have a bunch of motors salvaged from printers and scanners. I decided to use a DC motor as it would be easiest to interface.
Problem: DC motor? So how do you know if it’s a DC motor and how much DC?
Solution: Well, I usually count the wires and if there’s two wires coming out of the motor it’s probably DC. I have an adjustable DC power supply, so I turn it down to zero, hook up the motor and turn up the motor until it starts turning. Most DC motors will vary their speed with the voltage so you can keep increasing the voltage until it starts smoking or flies apart. NO, I take that back, don’t go that far.
By the way, DC motors will spin the opposite direction if you switch the power connections.
Problem: How do I connect the motor to the threaded shaft.
Solution: This DC motor has a small gear on it. On the threaded shaft, I cut it down to the frame size plus a little extra. I put two nuts on top and tightened them against each other so they wouldn’t slip. Now the nuts were bigger than the gear. I found some vinyl tubing that fit tightly over the motor gear but I couldn’t get it over the nuts. So I cut a couple of slits in the tubing, slipped it over the nuts and clamped it with a tie wrap. (See picture)
Problem: So I started putting it all together. Oops! I found out the microscope would hit the top sooner than desired. I wanted the microscope to be able to move about 6” above the base. There’s the OLD again.
Solution: Well, I took it apart and cut another half moon in the top so the microscope would have more clearance.
Problem: So the next problem was how to mount the motor. Hmm!
Solution: Basically all that is needed was some kind of plate so a couple of screws could hold the motor in place. Well, I came up with the ‘clever’ idea of using another piece of plastic since the guide shafts were sticking out anyway. Drilling was a little harder as I hadn’t thought of this when I did the first drilling. What I did was drill one of the guide holes then inserted a guide shaft through the top and through the new plastic. Then clamped the plastic to the top and drilled the second guide hole through the top hole.
The motor hole wasn’t critical as it just needs to allow the motor to turn freely.
Step 4: Electrical Assembly
So being a Geek, here is my schematic. This motor seems to be a 12Vdc motor, at least I needed about that much to turn the shaft. R1 is a potentiometer to adjust the speed.
The Up_Dn switch is a DPDT center off switch. That means it has three positions, on, off and on. Using this switch wired this way is a rather ‘clever’ way to switch directions. If the switch is straight out, there is no power. If the switch is up, the assembly will move up. If down, then down.
So I attached the pot and switch to a U shaped piece of metal I had from an old screen door.
Power Supply: For my circuit, I need 12Vdc at about 1Amp.
Caution: Most wall wort power supplies are marked with a voltage and current. Usually the voltage is a little higher than marked. In most cases this is not a problem as it will drop a bit under load. But I found that many will not allow anywhere near the current they’re supposed. It may be marked as 1.2A but will only supply about 0.5A. I don’t know why that is. Maybe they’re thinking peak current.
Anyway, I have a computer power supply connected to my workbench so have lots of power.
Astute Readers: So the astute reader may wonder why there is a 2.4 ohm 1 Watt resistor going across the potentiometer. Well, I didn’t think it was needed and I tried it without it. Unfortunately, when I tried it without it, the potentiometer was literally smoking and sparking!! That’s a good sign of too much current.
I don’t know what the potentiometer is rated at but I decided to add some resistance in parallel with the pot to share the current and decided on this 2.4 ohm 1W. The resistance is probably a little low as the assembly will always move when the power is applied unless it’s stalled.
Step 5: Operation and Thoughts.
Operation: First, I place the object to view on the base.
Connect the microscope USB to a PC.
Run the software.
Adjust the microscope position up or down with the switch.
While watching the display, manually adjust the focus wheel until picture is focused.
This does work a lot better than with the purchased stand.
The pictures are from the computer. The assembly pictures show the position of the microscope for each.
Issues with assembly: The main issue is that the plastic microscope holder piece doesn’t stay horizontal and sometimes binds. A lot of this is because the threaded shaft is not over the center of gravity of the piece.
Sometimes, the assembly moves pretty fast. I should change the resistor to a bigger value so it will slow down.
Issues with microscope: The microscope comes with four LEDs that can be adjusted. With my setup, I can’t use them at all as it just overwhelms the picture. I seem to have the best luck with no extra illumination and just room light.
Sometimes the focus wheel binds and I have to remove the microscope from the frame to get it too turn. It’s possible my assembly is squeezing it too much.
I will probably use this as is for a while. Some day I might change the resistor to get more control over the speed. And maybe try to mount the assembly better so that it doesn’t slant.
And maybe I’ll try taking the microscope apart to work on the focus.
But I doubt it. I’m Lazy and Old.