As part of our Op-Amp Challenge we’re seeing a wide diversity of entries showcasing the seemingly endless capabilities of these extremely versatile parts. Another one comes from [Joseph Thomas], who when faced with the need to measure the properties of an automotive spark plug, came up with a precision peak detector to hold on to the energy level used when firing it.
It starts with an op-amp buffer feeding a diode and capacitor. The capacitor is charged through the diode and holds the level, which can be read through another op-amp. Finally there’s an opto-isolated transistor to discharge the capacitor before a fresh reading is taken.
It’s a simple enough circuit but a very effective one. The op-amps used are bit old-school FET devices, but aside from the high impedance input their performance is hardly critical. Yet another op-amp circuit to hold in reserve should you ever need to perform this task.
[Duncan McIntyre] lives in the UK but participated in a secret Santa gift exchange for his Dutch friends’ Sinterklaas celebration. In traditional maker fashion, [Duncan] went overboard and created a miniature gym gift box, complete with flashing lights, music and a motorized lid.
[Duncan] used [TanyaAkinora]’s 3D printed tiny gym to outfit the box with tiny equipment, with a tiny mirror added to round out the tiny room. An ATmega328P was used as the main microcontroller to drive the MP3 player module and A4988 stepper motor controller. The stepper motor was attached to a drawer slide via a GT2 timing belt and pulley to actuate the lid. Power is provided through an 18V, 2A power supply with an LM7805 providing power to the ATmega328P and supporting logical elements. As an extra flourish, [Duncan] added some hardware audio signal peak detection, fed from the speaker output, which was then sampled by the ATmega328P to be able to flash the lights in time with the playing music. A micro switch detects when the front miniature door is opened to begin the sequence of lights, song and lid opening.
[Duncan] provides source on GitHub for those curious about the Arduino code and schematics. We’re fans of miniature pieces of ephemera and we’ve featured projects ranging from tiny 3D printed tiny escalators to tiny arcade cabinets.
Video after the break!
Continue reading “Get Pumped For This Miniature Gym”
A fully stocked freezer can be a blessing, but it’s also a disaster waiting to happen. Depending on your tastes, there could be hundreds of dollars worth of food in there, and the only thing between it and the landfill is an uninterrupted supply of electricity. Keep the freezer in an out-of-the-way spot and your food is at even greater risk.
Mitigating that risk is the job of this junkbox power failure alarm. [Derek]’s freezer is in the garage, where GFCI outlets are mandated by code. We’ve covered circuit protection before, including GFCIs, and while they can save a life, they can also trip accidentally and cost you your steaks. [Derek] whipped up a simple alarm based on current flow to the freezer. A home-brew current transformer made from a split ferrite core and some magnet wire is the sensor, and a couple of op-amps and a 555 timer make up the detection and alarm part. And it’s all junk bin stuff — get a load of that Mallory Sonalert from 1983!
Granted, loss of power on a branch circuit is probably one of the less likely failure modes for a freezer, but the principles are generally applicable and worth knowing. And hats off to [Derek] for eschewing the microcontroller and rolling this old school. Not that there’s anything wrong with IoT fridge and freezer alarms.
Continue reading “Junkbox Freezer Alarm Keeps Steaks Safe”