CdS cell

11 Articles

Make A Mean-Sounding Synth From Average Components

January 14, 2020 by 12 Comments

A while back, [lonesoulsurfer] stumbled upon a mind-blowing little DIY synth on YouTube and had to make one of his own. We don’t blame him one bit for that, ’cause we’ve been down that cavernous rabbit hole ourselves. You might want to build one too, after you hear the deliciously fat and guttural sounds waiting inside those chips and passives. Don’t say we didn’t warn you.

The main synth is built on five LM358 op-amps that route PWM through a pair of light-dependent resistors installed near the top. There are two more oscillators courtesy of a 40106 hex inverting Schmitt trigger, which leaves four more oscillators to play with should you take the plunge and build your own.

He didn’t just copy the guy’s schematic and call it good. He added [a 555-based arpeggiator that’s controlled with two homebrew optocouplers. These sound fancy and expensive, but can be bred easily at home by sealing an LED and an LDR inside a piece of black heat shrink tubing and applying a bit of PWM. With the flick of a toggle, he can bypass the momentary buttons and use the yellow knob at the top to sweep through the pitch range with a single input.

Although he doesn’t hold your hand through the build, [lonesoulsurfer] has plenty of nice, clear pictures of the process that nearly give a step-by-step guide. That plus the video demo and walk-through should get you well on your way to DIY synthville.

If this all seems very cool, but you’d really like to understand what’s happening as you descend into the rabbit hole, our own [Elliot Williams]’s Logic Noise series is an excellent start.

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Shedding A Bit Of Light On Some Logic

October 15, 2018 by 30 Comments

When it comes to logic technologies, we like to think we’ve seen them all here at Hackaday. But our community never ceases to surprise us with its variety and ingenuity, so it should be a surprise that [Dr Cockroach] has delivered one we’ve not seen before. Light logic doesn’t use the conventional active devices you’d expect such as transistors, tubes, or even relays. Instead, it uses LEDs and CdS cells to make rudimentary switches. So far there is a NAND, a NOR, and a set-reset latch that appears in the video below the break, and it is not inconceivable that much more complex devices could be crafted.

The CdS cell switch is not too far different in operation to a transistor, with the CdS cell forming half of a potential divider as a rough equivalent of a collector-emitter circuit, and the LED feeding its light to the cell and forming a rough equivalent of a base circuit. It would probably not form a very good analog of a transistor and it seems likely that is will not be the fastest of devices, but we applaud the ingenuity in coming up with it.

CdS cells are a component that seems almost to come from another era, redolent of childhood electronic kits from days of yore. It’s no surprise we don’t see them too often, though, they pop up in the occasional automatic sunglasses.

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Intuitive Musical Books Accompany Alzheimer’s Patients’ Memories

August 3, 2018 by 10 Comments

If you have a loved one with Alzheimer’s, you know how difficult it can be to hold a conversation with them that doesn’t constantly go in circles. A good way to keep them focused is to use conversation pieces like pictures and familiar objects from their past. Something particularly poignant might uncork a flood of memories.

Adding familiar music to these images can be doubly beneficial. [Annelle] found this out when she showed her mother a musical children’s book that plays nursery rhymes. Her mother’s face lit up with joy when she heard those well-known tunes, and her reaction inspired [Annelle] to explore the idea.  After a fruitless search for more mature musical books, [Annelle] and her husband [Mike] got to work making their own using hymns, spirituals, and pictures from [Annelle]’s travels with her mother.

Alzheimer’s is a pretty tough test for intuitive interfaces. Because of this, [Annelle] and [Mike] designed around the constraints of buttons and switches. Instead, the book uses light-dependent resistors mounted inside the back cover, and an increasing number of holes in each page. These photo cells are all wired to an Adafruit sound board, which figures out the active page based on the input voltage and plays the corresponding song.

Tilt switches inside the 3D-printed enclosure negate the need for a power button. The book is turned off when lying flat on a table, but it’s ready to rock in any other position. Turn past the break for an overview video and another that covers the page detection scheme.

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Lasers, Mirrors, And Sensors Combine In An Optical Bench Game

March 24, 2018 by 11 Comments

Who would have thought you could make a game out of an optical bench? [Chris Mitchell] did, and while we were skeptical at first, his laser Light Bender game has some potential. Just watch your eyes.

The premise is simple: direct the beam of a colored laser to the correct target before time runs out. [Chris] used laser-cut acrylic for his playfield, which has nine square cutouts arranged in a grid. Red, green, and blue laser pointers line the bottom of the grid, with photosensors and RGB LEDs lining the grid on the other three sides. Play starts with a random LED lighting up in one of the three colors, acting as a target. The corresponding color laser comes on, and the player has to insert mirrors or pass-through blocks in the grid to create a path to the target. The faster you hit the CdS cell, the higher your score. It’s simple, but it looks really engaging. We can imagine all sorts of upgrades, like lighting up two different targets at once, or adding a beamsplitter block to hit two targets with the same color. Filters and polarizers could add to the optical fun too.

We like builds that are just for fun, especially when they’re well-crafted and have a slight air of danger. The balloon-busting killbots project we featured recently comes to mind.

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