A versatile kit that can be configured to drive either constant voltage LED arrays or constant current LEDs. Use the kit to dim under-cabinet LED lighting using flexible LED strips or build your own LED desk lamp using High Brightness LEDs.
The majority of the circuit is identical for both types of LEDs. Two inexpensive NPN transistors and a few resistors are added to the circuit for constant current LEDs. It uses the ability of a MOSFET transistor to act either as a digital switch or linear current regulator.
Constant voltage LED arrays include built-in current limiting resistors. Typically these arrays come in a flexible tape form (such as Jameco part number 2128631) but may also be constructed from discrete LEDs and appropriate current limiting resistors (for example a string of 3 white LEDs wired in series with a 120 ohm resistor designed to operate at 20 mA with a 12 VDC power supply). When configured to drive constant voltage LED arrays, the dimmer circuit acts as a digital switch that turns on and off hundreds or thousands of times per second to modulate the LED brightness.
Universal CC/CV LED Dimmer - [Link]
New USB chip from FTDI supports the Android open accessory mode, what enables a straightforward connectivity of USB devices and saves a battery of an Android device.
To connect a device to a smartphone (tablet,…) or other Android OS device via a USB is at the time possible in 2 ways – by means of a USB OTG (On The Go) or via a so called „Android open Accessory“ mode. USB OTG was introduced to you in the article – USB OTG – rather to be a master than a slave. USB OTG functions very well with many external devices but this method has one substantial requirement – your smartphone must recognize a given external device – it must have a suitable driver installed (similarly like at PC). The problem is, that for many USB devices you mast a driver to your Android device, what can be problematic from various reasons – absence of a suitable driver, “locked” system (limited access rights) loss of warranty on an Android device, ….
As a solution of these problems the Android Open Accessory Mode arised, when the role changes upside down and an Android device communicates in the USB device (Slave) slave. It means that the Host role takes an external device, while eliminating a need to develop drivers and guarantees a trouble-free communication. It means that this mode is very suitable for development of new devices intended for operation with Android devices. At the same time, the USB bus is powered from a Host device at this mode, what saves the battery of an Android device. Usually an application in a given OS uses drivers to communicate with a USB device. However in this case no drivers are required – an Android device reads a set of strings describing a given device (producer, model, URL address …) what is able to automatically start an application after connection of a given device. USB communication itself uses 2 endpoints for input and output (Bulk IN and Bulk OUT). That´s why an Open Accessory mode is suitable for all kinds of devices – data producing (sensors, probes,…) but also for data receiving (printers, robots, …).
FT311D brings this solution into reality and functions as a bridge between an Android device and various serial interfaces. It is possible to choose from up to 6 interfaces what suits to perhaps all nowadays devices – UART, PWM, SPI Master, SPI Slave, GPIOS, I2C Master. A great advantage of FT311D is, that the producer – company FTDI provides an extensive development support, including the UMFT311EV development board, code examples and demo applications.
Detailed information will provide you the FT311 datasheet, FT311 WP_001 and FT311D Android programmer guide. Further files can be found on the http://www.ftdichip.com/Android.htm
In case of interest, please contact us at firstname.lastname@example.org.
FT311 – USB communication with Android devices without drivers - [Link]
JN Lygouras, University of Thrace writes:
The control circuit in Figure 1a allows you to manually adjust the power delivered to a load. By changing the setting of potentiometer R3, you change the phase angle at which the thyristor (Q3) fires (Figure 1b), thereby altering the load current’s duty cycle. The adjustment range is about 0 to 180°. Q3’s off time is linear with R3, but of course the resulting load power is not linear with R3.
555 timer triggers phase-control circuit - [Link]
Alan @ vk2zay.net build a simple gamma ray detector using a photodiode. He writes:
Gamma photons interacting with cheap photodiodes produce small current pulses which are easily amplified and allow detection of individual photon events. This offers the possibility of cheap, small and rugged radiation detectors of reasonable sensitivity. While not as sensitive as larger GM-tube detectors, this solid state device is still quite useful for determining if something is radioactive enough to be interesting/concerning.
Photodiode Gamma Ray Detector - [Link]
Here is a reference design of a pulse oximeter built around the dsPIC33 digital signal processor.
Pulse oximeter is a non-invasive medical device that monitors the oxygen saturation of a patient?s blood and heart rate. This application note demonstrates the implementation of a high-accuracy pulse oximeter using Microchip?s dsPIC® Digital Signal Controllers (DSCs) and analog devices.
App note: Pulse Oximeter using dsPIC33 - [Link]
Here’s a video describing CMOS current sources.
CMOS current source circuits are examined. The voltage versus current and layout are presented. The channel region versus the voltage/current curve is explained. The equation to calculate the Gate-Source voltage is given. The CMOS cascode current source is also explored.
App note: CMOS current source - [Link]
Series Hammond 1553 handheld enclosures has sprawled out with smaller relations.
Handheld enclosures of the 1553T series with a sufficient space for a keyboard and a display was introduced to you in our recent article HAMMOND 1553T enclosures – keyboard and display in your hand. Enclosure 1553T is ideal for many relatively bigger devices, but probably there will be many applications, for which the 1553T is a little bit too big. That´s why company Hammond enriched this series with smaller types – „TT“, i.e. 1553TT. Version TT has practically the same features like the „T“ version, but it is in about 4,5 cm shorter (and proportionally smaller are also other dimensions). A few centimeters difference maybe doesn´t seem to be big but in result it is a substantially smaller enclosure, which sits in hands excellently. The difference in sizes is best illustrated in attached pictures.
That´s why, thanks to smaller dimensions is the TT version suitable even for devices with smaller displays and with smaller demands for inner space of an enclosure. Also 1553TT series is available in a black and a light-grey color and also without or with a battery compartment. Because of smaller dimensions, the TT version has a space for only 2pcs of AA batteries, what is adequate, as smaller devices are supposed to be less power demanding. All 4 versions are incorporated into our stable stock offer, detailed drawings, including 3D views can be found in datasheets at particular types. On the Hammond website, you can also find CAD files and 3D models.
HAMMOND 1553TT – keyboard and display even for women´s hands - [Link]
By: Alex Danovich,President San Francisco Circuits
We live in an exciting time where we see a resurgence in electronics as a hobby. Mass production has wiped out a generation or two of kids learning to build radios from scratch with their mom or dad. In the good old days, not sure when, you had companies like Heathkit walk you through building a full size color TV at home, for example. “Yes, I made that!” you’d proudly exclaim to yourself after hours of work.
What’s causing this hobbyist resurgence?
- Television shows such as How it’s Made, Mythbusters and other programming on TLC.
- Websites such as instructables.com, hackaday.com, and specialized hobbyist blogs.
- Interest in RC cars, robotics, gaming, computers etc.
- Advent of Arduino boards, modules and free software.
- Open source software/hardware.
- The whole maker movement in general.
So what does this have to do with making circuit boards? Read the rest of this entry »
Programming the LPC810M021FN8 , a tiny 32 bit Cortex M0+
The LPC810M021FN8 is a very interesting MCU in a 8 pin DIP package, designed to replace its 8 bit counterparts, ideal for hobbyist breadboard or through-hole printed circuit board (PCB).Being such a small and limited MCU, it has met a mixed reception since its announcement by NXP.Some argue that 8 bit processors are still up to the job making this one redundant or simply not attractive, preferring the similarly priced and already extensively used alternatives.For others the novelty of having a 32 bit MCU on such a tiny and easy to use DIP package is enough to have their attention.
Programming the LPC810M021FN8 - [Link]
Luca builds a controller to adjust speed and rotation direction of a stepper motor:
Using the controller, you can adjust the speed (from 0 to 70 RPM, revolutions per minute) and the rotation direction. On the LCD are displayed the actual speed, direction and a progress bar.
Allegro A4988 and Arduino - [Link]