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10 Sep 2014

Stanford engineer aims to connect the world with ant-sized radios.

A Stanford engineering team has built a radio the size of an ant, a device so energy efficient that it gathers all the power it needs from the same electromagnetic waves that carry signals to its receiving antenna – no batteries required.

Designed to compute, execute and relay commands, this tiny wireless chip costs pennies to fabricate – making it cheap enough to become the missing link between the Internet as we know it and the linked-together smart gadgets envisioned in the “Internet of Things.”

Stanford engineer aims to connect the world with ant-sized radios - [Link]

9 Sep 2014



A USB port is a great power source for charging a single cell Lithium-Ion battery. It is capable of supplying a maximum of 5.25V and 500 mA. The circuit above is a USB powered single cell Li-Ion battery charger. LM3622 is used as the controller. This special purpose IC has a precise end-of-charge control and low battery leakage current about 200nA.  S1 and S2 select the low voltage detect enable/disable.  The low voltage detection is handy for conditioning a deeply discharged battery with a low current stage, to prepare it for the full charge cycle.

LM3622 Li-Ion USB Battery Charger - [Link]

9 Sep 2014

How Ferrite Beads Work – EMI Suppression - [Link]

9 Sep 2014


by Marian Stofka:

Standard optocoupler speed is limited mainly by the relatively slow response of the phototransistor. This Design Idea adds components to the LED drive side to speed things up.

R1 is the original LED resistor, as used before the extra circuitry was added. Here however, its value can be higher, as the turn-on speed is determined mainly by the added circuit. You can thus save power, and also drive the LED with a less powerful driver.

Optocoupler speed-up also reduces power consumption - [Link]

9 Sep 2014


Clamp multimeter UT204 measures reliably even in real conditions of nowadays mains supplies and for an affordable price moreover.

UT204 from company UNI-Trend is a near relative to the UT203. multimeter. Already UT203 provides a lot of user comfort and a very pleasant feature – measuring of a DC current without interrupting a measured circuit. However UT204 is different from its “weaker” brother in one essential thing – it enable measuring of a true RMS value of alternating signals (TRMS).

As we know, usual multimeters usually deploy a simple rectifier and an RC cell and they´re calibrated to show an effective value of AC voltage – supposing an ideally sinusoidal shape of a measured variable.

In many cases, a non-TRMS multimeter is fully sufficient, but still more frequently we meet devices, which by their power consumption significantly deform originally sinusoidal shape of a mains line voltage. A vast majority of new devices is equipped with switch-mode power supplies deforming a sinusoid, as they draw current for charging of input capacitors mainly on a top of a sinusoid. This situation is partially better at power supplies with a power factor correction (PFC), but even in these cases it´s never an ideal load. At any difference from an ideal sinusoid the accuracy of a common meter significantly drops down and the error can exceed tens of percents. Similar situation is also at various DC/AC inverters (for example 12VDC/230VAC), whose output is usually only an approximated sinus.

That´s why if exact measurement matters to us, it´s more certain to measure by a device equipped by a TRMS measurement. There are many types with this function on the market, and in a segment of clamp multimeters it´s for example the above mentioned UT204, which moreover offers a lot of other functionality for an excellent price.

Detailed information and comparison of UT203/ UT204 will provide you the UT204 datasheet and the UT204 datasheet and UT203-204 user guide. We keep Uni Trend UT204 as a standard – immediately available item.

UT204 is able to measure DC current and also True RMS - [Link]

9 Sep 2014


Elmars Ositis has been working on a simple constant current driver:

In my previous post, I slapped together a quick LED lighting solution for my workbench… but it is truly a hack. What I really want to do is make a simple constant current driver, so the power LEDs can be used in other projects. One of those projects is an LED swimming pool light. It needs to be running at maximum brightness and low cost.

After much digging and testing, I found a simple circuit using a power FET, an OP Amp and 0.5 ohm resistor.
This simple circuit accepts a VCC up to 32v (limited by the Op-Amp). The 78L05 regulator provides a stable 5v reference and R1 is a potentiometer serving as a voltage divider, with the output on pin 2 serving as a reference voltage for the basic LM358 Op-Amp.


Simple constant current driver for a high power LED - [Link]

9 Sep 2014


by elektor.com:

Adding to their ever growing family of power supply regulators Linear Technology have introduced the LTC3807 step-down switching regulator DC/DC controller driving an all N-channel external synchronous power MOSFET stage. The chip uses a constant frequency current mode architecture allowing a phase-lockable frequency of up to 750 kHz.

The chip draws just 50 μA no-load quiescent current and an OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3807 features a precision 0.8 V reference and power-good output indicator.

Low-loss Step-down Regulator - [Link]

8 Sep 2014


by embedded-lab.com:

This Arduino Nano controlled solar battery charger can charge a standard lead acid 12V battery and runs with 90% efficiency under 70ᵒC (158ᵒF). The circuit can take up to 24V input from the solar panels. The maximum power point tracking is implemented in the circuit by measuring the output voltage and current from the solar panel to get the maximum possible power from it.

Solar battery charge controller - [Link]

8 Sep 2014


Meter clock: keeping “current” time. Read more about the clock:

I’ve seen a few meter clocks in my travels of the web, and I love the idea. A few days ago, I decided that I must have one of my own. Such began the “How to do it” pondering cycle. I had seen builds where the face plate of the meter is replaced. This works, but I wanted to try and find a way to do it without modifying the meter, if possible. After some more ponderation, I came up with what I think is a serviceable idea.

I came across this style of milliamp meter on Amazon. They’re not quite 0-60 mA, but the 0-100 mA (a 0-20mA meter for the hours) is close enough. And they were cheap. So yay.

Part of my requirements were that the clock run off of an Arduino Pro Mini I had lying around, and with minimal additional parts. In order to drive the meters with some degree of precision, I would use the PWM pins to vary the effective voltage across a resistor in series with the meter. This would, by the grace of Ohm’s Law, induce a current that, based on the PWM duty cycle, would be scaled in such a way as to move the needle on the meter to the corresponding hour, minute, or second.

One minor issue came up in the form of the max current the GPIO pins on the ATMega328 chip can source/sink. The pins can source/sink a maximum of 40mA, a bit far from the 60mA needed for the minutes and seconds meters. Enter the transistor.

Using a simple NPN transistor switch circuit, I was able to provide the current for the minute and second meters from the 5V supply. The PWM signals switch the respective transistors on and off, effectively varying the voltage across the resistors in series with the meters.

The resistor between 5V and the meter is actually 2 1/4 watt 100 Ohm resistors in parallel for an effective resistance of 50 Ohms. The two in parallel was necessary as 5V x 0.06A = 0.3W (more than 0.25 that a single 1/4W resistor can handle safely).


Meter clock: keeping “current” time - [Link]

8 Sep 2014


Ken Shirriff has a great post on his blog about reverse engineering how a 7805 voltage regulator works:

Under a microscope, a silicon chip is a mysterious world with puzzling shapes and meandering lines zigzagging around, as in the magnified image of a 7805 voltage regulator below. But if you study the chip closely, you can identify the transistors, resistors, diodes, and capacitors that make it work and even understand how these components function together. This article explains how the 7805 voltage regulator works, all the way down to how the transistors on the silicon operate. And while exploring the chip, I discovered that it is probably counterfeit.


Reverse Engineering A Counterfeit 7805 Voltage Regulator - [Link]





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