How CMOS Works: MOSFETs, JFETs, IGFETS and More

CMOS opened the door for many if not most of the properties needed for today’s highly integrated circuits and low power portable and mobile devices. This really couldn’t happen until the speeds and current drive capabilities of CMOS caught up to the other technologies, but catch up they did.

Nowadays CMOS Small Scale Integration (SSI) logic families, I.E. the gates used in external logic, offer very fast speeds and high current drive capability as well as supporting the low voltages found in modern designs. Likewise the Very Large Scale Integration (VLSI) designs, or Very Very Large Scale if you like counting the letter V when talking, are possible due to low power dissipation as well as other factors.

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Motion Sensing Water Gun Tweets Photos To Embarrass Enemies

[Ashish] is bringing office warfare to the next level with a motion sensing water gun. Not only does this water gun automatically fire when it detects motion, but it also takes a photo of the victim and publishes it on Twitter.

This hack began with the watergun. [Ashish] used a Super Soaker Thunderstorm motorized water gun. He pulled the case apart and cut one of the battery wires. he then lengthened the exposed ends and ran them out of the gun to his control circuit. He also placed a protection diode to help prevent any reverse EMF from damaging his more sensitive electronics. The new control wires run to a MOSFET on a bread board.

[Ashish] is using a Lightblue Bean board as a microcontroller. The Bean is Arduino compatible and can be programmed via low energy Bluetooth. The Bean uses an external PIR sensor to detect motion in the room. When it senses the motion, it activates the MOSFET which then turns on the water gun.

[Ashish] decided to use Node-RED and Python to link the Bean to a Twitter account. The system runs on a computer and monitor’s the Bean’s serial output. If it detects the proper command, it launches a Python script which takes a photo using a webcam. A second script will upload that photo to a Twitter account. The Node-RED server can also monitor the Twitter account for incoming direct messages. If it detects a message with the correct password, it can use the rest of the message as a command to enable or disable the gun.

Play Robotic Bongos using your Household Plants

[Kirk Kaiser] isn’t afraid to admit his latest project a bit strange, being a plant-controlled set of robotic bongos. We don’t find it odd at all.  This is the kind of thing we love to see. His project’s origins began a month ago after taking a class at NYC Resistor about creating music from robotic instruments. Inspired to make his own, [Kirk] repurposed a neighbor’s old wooden dish rack to serve as a mount for solenoids that, when triggered, strike a couple of plastic cowbells or bongo drums.

A Raspberry Pi was originally used to interface the solenoids with a computer or MIDI keyboard, but after frying it, he went with a Teensy LC instead and never looked back. Taking advantage of the Teensy’s MIDI features, [Kirk] programmed a specific note to trigger each solenoid. When he realized that the Teensy also had capacitive touch sensors, he decided to get his plants in on the fun in a MaKey MaKey kind of way. Each plant is connected to the Teensy’s touchRead pins by stranded wire; the other end is stripped, covered with copper tape, and placed into the soil. When a plant’s capacitance surpasses a threshold, the respective MIDI note – and solenoid – is triggered. [Kirk] quickly discovered that hard-coding threshold values was not the best idea. Looking for large changes was a better method, as the capacitance was dramatically affected when the plant’s soil dried up. As [Kirk] stood back and admired his work, he realized there was one thing missing – lights! He hooked up an Arduino with a DMX shield and some LEDs that light up whenever a plant is touched.

We do feel a disclaimer is at hand for anyone interested in using this botanical technique: thorny varieties are ill-advised, unless you want to play a prank and make a cactus the only way to turn the bongos off!

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Automatic Plant Care Minus the Microcontroller

Plants are a nice addition to most any habitat. Many of them bear flowers or attractive foliage, some of them help filter the air, and others, like aloe vera, have medicinal properties. While some plants require very little care, they all need a little moisture at some point. Overall, plant care is a bit fiddly: water them too much and you run the risk of root rot; water too little and risk death by dehydration. Hackaday alum [Kevin Darrah] would prefer not to gamble with either condition, and so in the course of a weekend’s time, he constructed a solar-powered automatic plant watering system from components he had on hand.

While he likely had a microcontroller or two lying around, he didn’t use one. His is a system of MOSFETs that trigger a motorized pump from one of those automatic bug spray bottles to draw from a reservoir and water the plant. The solar panel charges a bank of 6800µF capacitors that [Kevin] took out of an old receiver. When the desired charge is reached, the small soil sensor module is powered, assessing the moisture level. If the level is below the threshold determined by a trimmer pot, the power from the capacitor bank is dumped to the water pump and his plant gets a drink.

[Kevin]’s design deals nicely with the possible pitfalls of solar power. He’s included a 0.1µF cap to ensure latching through the system, and added a bleed resistor so that the pump is never powered unnecessarily. After running it for a couple of days, he’s already seeing moisture regulation in the soil. His complete demonstration and theory of operation is after the break. If you’re into solar power but aren’t quite ready to ditch the µC, check out this Arduino-controlled solution for thirsty tomatoes or this PIC-powered plant pacifier.

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Triggering Remote Fireworks with an Arduino and an Android


With Canada day and Independence day fast approaching, some makers are looking towards setting up their own fireworks to shoot off in celebration – sure you could use a match or lighter… or you could crack out your trusty Arduino and a cellphone! (translated)

To ignite the fuse, [Oscar] is using a short length of Nichrome wire which is controlled via a Mosfet by the Arduino. To control the Arduino he’s using ArduDroid with a Bluetooth module. The app lets you trigger the various digital and analog outputs, and send and receive data.

Stick around to see a few different demonstration videos of the circuit, testing, and launching some little bottle rockets!

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Hackaday Video: Safe Area Operation for Components (and Helicopters)

We’re back and this time talking about Safe Operating Area also called Safe Area Operation (SAO) which is short for the combination of things that can conspire to ruin your design. We also talk about helicopters.

Why take all of this time to discuss SAO you might ask, and what is that business about helicopters? Depending on the design there may be quite a bit of tedious math involved and sometimes there is just no avoiding it. Alternatively if you can get a feel for when math is and is not critical (based on design choices), it should be easier to get your next project up and running while still obeying the rules of the road.

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Fail of the Week: Frying FETs with 500mA


When [Simon] fried his 3A rated FET with just 500mA of current he wrote it off to an inability of the SOT23 package to dissipate the heat without a heatsink. For the next iteration of the project he upgraded to a 12A rated part. Luckily he decided to test the circuit one more time before sending his board off for fab. He threw together this constant current load test which led him to discover his failure.

The switching circuit, which was for his home security system project that we’ve seen at least twice, worked just fine up to 500mA. But when he drove it above that threshold the package quickly warmed up. It got so hot that it actually reflowed its solder joints! The problem has to do with oscillation, but even with further testing he couldn’t get the FET to reliably shut off all the way. Take a look at his fail write-up linked at the top and then let us know some possible remedies for the situation.

2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.