When the circuit is powered up, all of the transistors are off and stay off. C1 gets pulled up to Vp. When the switch is pushed, Q3 and Q2 turn on, since their base is pulled up. Q1 and Q4 are in turned on as well. Q1 keeps Q2 turned on and Q2 keeps Q3 turned on and Q3 keeps Q4 turned on. Q4 supplies current to the load. When Q2 is asserted it keeps pin 1 of SW1 at ground.
When the switch is pulled low again, the base of Q3 is tied to ground, because Q2 is on, and the chain is broken an all of the transistors turn off.
C1 and R1 and R5 form the time constant for the debounce circuit. Adjust these values for an appropriate debounce time.
Latching Momentary Switch for breadboard - [Link]
Mizchief100 @ instructables.com writes:
This project was my take on a DIY visual impairment aid that uses haptic and sound feedback. Basically it uses a distance sensor to measure how far objects are from it and then it beeps/vibrates accordingly (far away is slow vibrate/long beep delay and close up is fast vibrate/quick beeps). Real quick I’d like to acknowledge that I’m not the first to do something like this, but I have added many things to it that are different from designs I have seen. This isn’t being used for commercial purposes but just as a guide for others to make them for people who would actually benefit from having them.
VIA (Visual Impairment Aid) - [Link]
kmpres @ instructables.com writes:
My urge to build this project came when my wife’s car refused to turn over after a three day weekend away. Here in Tokyo, during winter, the temperature can drop to the low 20’s (F) at night and since we have no garage, her car just has to endure the cold as best it can. Many people don’t realize that you don’t have put up with repeated jump-starts or run to the nearest garage and plunk down 7,500 yen ($85) for a new battery every time this happens. Your old battery may just have built up a layer of lead sulphate crystals on its plates and that is preventing the acid from contacting them over their full surface area. This is caused by subjecting the battery to long periods of insufficient charge, as in the cases of unplugged golf carts over the winter, infrequently used automobiles, and PV systems that don’t get enough sunlight to charge their batteries. The result is a great reduction in the battery’s ability to produce electricity.
Desulfator for 12V Car Batteries, in an Altoids Tin - [Link]
mattthegamer463 @ instructables.com writes:
If you’ve ever been designing a circuit and had to experiment with different values of caps and resistors, you probably didn’t like it much. It can be a hassle to switch out components over and over, trying to find the right combination to suit your needs. With RC filter circuits, it can be quite difficult to determine what resistance and capacitance you need to get the filtering attributes you want. With a Selection box such as this just a turn of a knob can test many different values.
Build a Resistor/Capacitor Selection Box - [Link]
Vladimir Rentyuk writes:
A TL431 shunt regulator is a perfect choice for many applications. You can use it as a comparator with hysteresis by taking advantage of its inner voltage reference along with few additional components. You can use this comparator with hysteresis, like a Schmitt trigger, as a simple battery monitor (Figure 1). You calculate the threshold voltage, VT+, of this comparator as VT+=VREF×(1+R1/R3), where VREF, the internal reference voltage of shunt-regulator TL431, is 2.5V.
Shunt regulator monitors battery voltage - [Link]
Peter T Miller writes:
Like other simple, single-cell lithium-ion battery chargers, Microchip’s MCP73812 provides no means of indicating the charging status. You can remedy this situation by adding four components (Figure 1). Add one more LED, and you also get a charging-complete indication. This two-LED configuration has the added benefit that one of the LEDs is always on, providing an indication that the charger is powered.
Add charging status to simple lithium-ion charger - [Link]
Mats of GerrySweeney’s inexpensive Decade programmable resistor:
I bought this 7-decade resistor box from Gerry Sweeeney for $18. It’s a really nice little cheap tool – much cheaper than the models with switches or thumbwheels that usually are 5-10 times as expensive as Gerrys version.
Decade resistor box with jumpers - [Link]
T.K. Hareendran writes:
All items stored in a deep freezer will thaw out if, for some reason, the temperature inside the freezer rises to the thaw point. However, a freezer monitor alarm can warn you of the rising temperature before the thaw point is reached.
This simple circuit is powered by regulated 9V and built around a few discrete components that are readily available in the market. Current consumption of the circuit is only a few milliamperes in idle state. So you can also use a 9V 6F22/PP3 type compact battery for powering the circuit.
Freezer Monitor Alarm - [Link]
I’ve been an electronics hobbyist for many years, so I’ve used and even built my share of resistance decade boxes. Each one consisted of rotary switches with labels identifying a different power of 10 for each switch. You “dialed up” the desired resistance by turning the appropriate knobs to add up to the target resistance value.
Well, I’m also a computer geek, so I got the crazy idea to build a decade box using DIP switches (instead of rotary switches) and binary values (instead of decimal values). Each switch represents a power of 2 and the resulting resistance equals the combined value of the “ON” switches.
Binary Resistance Decade Box - [Link]
What was technology like inside a 1994 Motorola MicroTAC GSM mobile phone?
EEVBlog #492 – Vintage Motorola MicroTAC Mobile Phone Teardown - [Link]