Bulk 4-Cent Photocells: What Shall We Make?
erco
Posts: 20,254
Fugget about Fitty Cent. I got twenny photocells for 80cent: http://www.ebay.com/itm/261420488934
Sure, old school. Slow response. Uneven color response. But they're classic. Vintage. Retro. Embrace their idiosyncrasies. If you can't fix it, feature it! At 4 cents each, we should be using ten in every project just for sport. Make a 100x100 array for an image sensor. Make an 80-cent necklace out of 20 in series. Sun trackers. Line sensors. Room guards.
Did we ever decide if these are RoHS compliant or not? If not, here are 50 phototransistors for $4.45 (9 cents each): http://www.ebay.com/itm/10pcs-50pcs-5mm-940nm-IR-detector-sensor-Infrared-Phototransistor-/181500082240
Or swing the other way (environmentally) and stock up on real old school toxic mercury switches while you can: http://www.ebay.com/itm/10PCS-3MM-Mercury-Switch-Total-10PCS-/191130300666
And throw in a few 19-cent lasers for good measure: http://www.ebay.com/itm/10pcs-650nm-6mm-3V-5mW-Laser-Dot-Diode-Module-Head-With-Red-Dot-B-S5-/271890579637
Now what are we gonna build, fellas? Let's put our heads together and come up with something good. Duane made his nifty low-res imager a few years back. Hopefully he'll chime in with some good ideas. I'm just the enabler (and resident low-tech cheapskate).
Sure, old school. Slow response. Uneven color response. But they're classic. Vintage. Retro. Embrace their idiosyncrasies. If you can't fix it, feature it! At 4 cents each, we should be using ten in every project just for sport. Make a 100x100 array for an image sensor. Make an 80-cent necklace out of 20 in series. Sun trackers. Line sensors. Room guards.
Did we ever decide if these are RoHS compliant or not? If not, here are 50 phototransistors for $4.45 (9 cents each): http://www.ebay.com/itm/10pcs-50pcs-5mm-940nm-IR-detector-sensor-Infrared-Phototransistor-/181500082240
Or swing the other way (environmentally) and stock up on real old school toxic mercury switches while you can: http://www.ebay.com/itm/10PCS-3MM-Mercury-Switch-Total-10PCS-/191130300666
And throw in a few 19-cent lasers for good measure: http://www.ebay.com/itm/10pcs-650nm-6mm-3V-5mW-Laser-Dot-Diode-Module-Head-With-Red-Dot-B-S5-/271890579637
Now what are we gonna build, fellas? Let's put our heads together and come up with something good. Duane made his nifty low-res imager a few years back. Hopefully he'll chime in with some good ideas. I'm just the enabler (and resident low-tech cheapskate).
Comments
"Light Sensitive Inductor"
Use it as one element of a voltage divider with the junction fed into an ADC. Easy-peasy.
Oops.
I've been Ebay hoarding even more than usual, stocking up on breadboards, battery boxes, batteries, photocells, thermistors, transistors, resistors, mosfets, pots, relays, ultrasonics, soil sensors, voltmeters, servos, remotes, IR receivers, etc.
Or with a capacitor and measure the r/c time constant.
Sweet, same here! Takes forever to get stuff. Batteries are a bit of a hold up right now. Rechargeable AA's are expensive and awkward. Cheap lipos and chargers seem ok for some age groups but certainly not all. I dislike alkaline but will have to start somewhere.
I find tools to be equally important. What about a cheap DMM? There are a lot out there, this one has a buzzer and is small - http://www.ebay.com/itm/Mini-Digital-Multimeter-with-Buzzer-Voltage-Ampere-Meter-Test-Probe-DC-AC-LCD-/131452681513?pt=LH_DefaultDomain_0&hash=item1e9b30bd29
Alibaba's massive lot quotes for parts seem to be only pennies cheaper than individual eBay auctions. I'm looking for a good rewards card to put the eBay stuff on the hopefully bring the price down even lower. I hope parts start showing up soon. I'm glad we're bouncing stuff back and fourth, it will help me tremendously.
You know there will be SD vs LA competitions! Some kind of navigation challenge for time maybe?
I also picked a name
I do like that multimeter with the continuity buzzer, very handy. Don't have that one! I'll have to blow up one of my HF freebies first to justify spending $4.
Edit: I pulled the trigger on one. This hoarder can't wait. Will probably order more.
That's very handy for students, but of course just teaching "how to not destroy your new multimeter" takes an hour that I don't have...
Plan to stock up on any parts which can be destroyed. They will be.
These cheap test leads can accelerate the inevitable "magic smoke release": http://www.ebay.com/itm/10pcs-Double-ended-Test-Leads-Alligator-Crocodile-Roach-Clip-Jumper-Wire-SU-/191374054576
http://www.rsjtechnical.com/WhatareRoHSexemptions.htm
CdS cells used in specifica applications were once exempted from ROHS, but the exemption appears to have expired. The exemption might have been renewed; it can be hard to find updated information.
Still, this applies to EU, and largely for finished goods. Individual components for the purpose of education and research (generally) fall outside the rules. Don't quote me on it, but I'd think that lot of 10,000 cells you just ordered is probably A-OK, should you move to France or Germany.
Here's a photo of the LED array I made.
In case it's not clear, the array is displaying the image seen by the black and white camera held in my fingers in the top left of the photo. The "HI" on the whiteboard can (hopefully) be seen on the LED array. I used Hanno's method of capturing video with the Propeller.
I suppose one could make an imager with an array of photoresistors but it would sure take a lot of work to wire and program.
I'm not sure what demon possessed me to hand solder my 12 x 10 LED array. Here's the backside of the array.
The stack of chips in the photo are '595 shift registers. I used four data lines (with a PASM driver) to reduce the refresh period of the screen.
One could stack some ADC chips and read an array of photoresistors. You'd need some sort of lens to focus and image on the sensors. A pin hole would also work but I'm not sure if you'd get enough light to produce an image if a pin hole were used.
An array of photoresistors would probably make a good teaching aid. It could be helpful when explaining how digital cameras worked.
I'm sure there are other interesting applications for an array of photoresistors. The photoresistors could be arranged in a circle around a sundial in order to digitize the information from the shadow. It could be part of a retro futuristic digital clock which only worked when the sun was up. You might as well make it solar powered while you're at it.
@Andy,
Robotics with the Boe-Bot v2.2 has a section on using photoresistors in a voltage divider on page 197. (Here's a link to version 2.2 pdf.)
The part labeled "Vo" would be connected to one of an ADC chip's input pins (or a sigma-delta circuit). The bottom resistor in the divider may need to be changed depending on the photoresistor's resistance range.
Semi-circle, actually. Lessee: Suppose 6 am to 8 pm is 14 hours, times 10 (six-minute precision) says 140. I better get 150 or maybe 200. Gonna take one helluva shift register.
You'll want 141 to include the zeroth (6am) position.
You should be able to do it with two '595 and two '165 shift registers.
You'd need to use resistor values, which allowed the sundial's shadow, to cause a change in the voltage out, of the voltage divider, so it moved from one side of the '165's input threshold to the other. (I hope that makes sense.)
Two of each type of shift register should allow you to monitor 256 photoresistors.
-Tor
Looks to me like the eBay DVM is almost identical to the HF freebie. Some differences, but I'd say they're probably equivalent.
erco,
I hope you're not the guy at our local flea market that tries to sell HF meters, tape measures, etc. (all the freebies) for twice the "original" HF price. Week after week he has the same items...
Walter
Say and icosahedron with 20 photo cells pointing in 20 directions.
Should be good for detecting some kind of motion with some degree of directional accuracy.
Kind of spooky anyway.
Nice cover of a song by one of my favorite keyboardist and composers, Yanni:
The song covered starts at 1:00:40
https://www.youtube.com/watch?v=NulxeH5WaaI