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]
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]
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]
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]
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]
by Vadim Panov:
Back when I was only starting to dabble in electronics, I needed a project that would meet the following requirements:
simple to make;
original (i.e. done entirely by myself from scratch);
containing a microcontroller;
and maybe the most important of all, useful. I’ve had enough devices I assembled just to dismantle the whole thing a month later.
The thing I came up with at the time was a light swich for my room controlled over an IR remote from TV. Remote that I had used RC-5 protocol, hence the firmware is suited for any RC-5 compatible remote.
Everyone is familiar to the everliving problem with switching the lights off in your room before going to bed and stumbling back across the room. The IR switch I describe here solves that problem, and I can definitely tell that this project was a success – I am still using it with no regret.
Infrared remote controlled light switch with ATTiny2313 - [Link]
A stable single transistor sine wave generator, that works with many values of input voltage. In PartSim you can easily change the value of the resistors and capacitors and observe the effect on the frequency of the oscillator. If you are manually calculating the frequencies, make things simpler by keeping the values of the resistors and capacitors equal (R5=R6=R7 and C1=C2=C3). You can see in the simulation that it takes a while to begin oscillating, and in ideal conditions it would need a signal to start oscillating, however in practice, noise begins the process without it.
2N2222 Phase Shift Oscillator - [Link]
by drmpf @ instructables.com:
The first instructable shows you how to use the free pfodDesigner available on GooglePlay to design Android menus to switch Ardunio outputs on and off from your Android mobile, without you having to write any program code at all. The Fish Tank picture above shows the example designed in this instructable.
The example project shown here is suitable for complete beginners. This instructable does not require any soldering and No coding experience is required.
Once you have finished this instructable you will be able to design whatever menus you need to switch Arduino outputs on and off. When you have completed the second instructable (to be posted later) you will be able to switch real things on and off from your Android mobile, via relays connected to Arduino’s digital outputs.
Code generator for custom Android/Arduino menus - [Link]
by BrittLiv @ instructables.com:
Heating things up is one of the most performed tasks in a lab. Quite a lot of times it is not enough to simply hold something at a certain temperature, but the rate at which something is heated and for how long is just as important. Especially when you try to develop catalysts for chemical processes, the temperature program and exact temperature control is crucial and you probably do not want to stay in the lab for 16 hours to manually adapt your temperature program. Unfortunately, programmable temperature controllers that can automate processes are really expensive. So I decided to build a highly customizable controller that is able to run temperature ramps and read multiple different temperature programs from a SD card. It also provides a logging function on the SD card that allows you to evaluate the resulting temperature profile after running a program.
Programmable Temperature Controller + Hot Plate - [Link]
Ondřej Karas of DoItWireless writes:
We described simple method, how to drive modellers servo. Today, we are going to try to drive this servo from potentiometer connected to TR module ADC. It is reaction to forum thread where is discussion about airplane model control possibility.
Wireless servo controller II - [Link]