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]
UV resin based mUVe 3D Printer releases source files:
The mUVe 1 3D Printer, an open UV resin based 3D printer was successfully funded on indiegogo back in April. As estimated, the first Ultimate kit was shipped out on Jun.20. Last weekend the team has completed building and shipping all of the Ultimate kits. Meanwhile Dean Piper, the maker behind the mUVe 1 3D Printer project, has shared all of the source material on their website
UV resin based mUVe 1 3D Printer source files released - [Link]
Mats continues his challenge of designing one PCB every week. In week 12 he came up with BB Prince, a small multi-purpose utility for your solderless breadboard:
This PAW is a small utility board for your breadboard that have some of the most common things you need when building a microcontroller-based project on the breadboard. It’s a small (2.5×1.5cm / 1×0.6”) PCB with a Power Led, a Reset button with a pullup and goes low when pressed, a Signal button with pulldown that goed high when pressed and two general Indicator Leds that are connected to ground via resistors.
BB Prince – breadboard utility PCB - [Link]
Boris Landoni writes:
It’s small but packed with features. The GSM alarm we present today, sports a PIR motion sensor, can be battery operated and it’s capable to communicate via GSM. It can transmit alarm conditions and receive commands from remote. It’s also capable to indicate problems such as is insufficient voltage supply or tampering.
It’s not so conventional for antitheft system: to integrate a movement sensor, a PIR motion sensor and a temperature probe in a single appliance: all this accompanied by an SMS sending GSM / GPRS module. This circuit was born as a very versatile, ready to use, built-in alarm system: no installation is required, you can just drop it and it’s ready to work. It’s not by chance that is designed to be battery operated: it also features a battery state control to check the power.
GSM Multifuction Alarm with SIM900 - [Link]