This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1.
The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its reset pin becomes high. When the Laser / IR beam breaks, current through the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.
A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.
555 Photodiode alarm – [Link]
VoCore is an open hardware runs OpenWrt. It has WIFI, USB, UART, 20+ GPIOs but size is only one inch. It helps you make a smart house or study embedded system.
VoCore is a coin-sized Linux computer with wifi. It is also able to work as a full functional router. It runs OpenWrt on top of Linux. It contains 32MB SDRAM, 8MB SPI Flash and using RT5350(360MHz MIPS) as its heart. It provides many interfaces such as 10/100M Ethernet, USB, UART, I2C, I2S, PCM, JTAG and over 20 GPIOs but its size is less than one square inch(25mm x 25mm).
VoCore: A coin-sized Linux computer with wifi – [Link]
Mastro Gippo writes:
I just finished wrapping up an article about a small project I did in Shenzhen during the HackerCamp with Ian. I hope you find it interesting and feature it!
Making stuff in Shenzhen – The Grillino – [Link]
by Roy McCammon:
The traditional three op-amp differential amplifier’s signal to noise ratio can be improved by 6dB by adding a resistor and slightly changing the connections. There is a trade-off though: The traditional topology has a high input impedance, whereas the low-noise version has a lower input impedance.
Differential amp has 6dB lower noise, twice the bandwidth – [Link]
Ioannis Kedros writes:
Another quick project for today! How all started? A few hours ago I took a delivery box with few high resolution LCD’s on it. The box was made of foam material and was covered with dirty (from the delivery across two continents) yellowish tape.
To begin with, in order to open the box I had to remove half of this tape and by “playing” with the box I manage to remove everything without to damage it! Yes, the tape was strong enough to tear apart everything! The result is the one below
Rescuing a foam box – [Link]
By Tessel Renzenbrink:
David Hunt built himself a working mobile phone using a Raspberry Pi and off-the-shelf components. The main building parts are the $35 Adafruit Touchscreen interface and a $48 SIM900 GSM/GPRS module for making phone calls. In total the phone costs $158 to build.
PiPhone: Turning Your Pi into a Phone – [Link]
MotherBone™PiOne™ is a peripheral motherboard for BeagleBone Black & Raspberry Pi providing safe I/O expansion for Linux based systems
We were evaluating BeagleBone Black and Raspberry Pi for low cost control systems when we discovered that the modules, as shipped, were fundamentally unusable for anything other than connecting to your PC and programming.
We created a multi-tool: an all-in-one 3.5″ peripheral voltage isolating motherboard for the BeagleBone Black and Raspberry Pi Model B computers and expanded out and isolated all of the default configuration pins that were not being used by BeagleBone Black internal resources. We also created two different on-board communication links between Raspberry Pi and BeagleBone Black for advanced control functions. Now you are able to run both modules individually or simultaneously in the real world.
MotherBone PiOne on Kickstarter – [Link]
by Francesc Casanellas:
This design was done to get a sealed keypad for very wet environments (in my particular case, showers for swimming pools). The keypad needed to be able to detect slight pressure on a stainless steel plate 0.4mm thick. Apart from water protection, the solution offers an esthetical finish, as the user side is absolutely flat, with nothing visible other than the silkscreened print. Another advantage of this type of keypad is that it is vandal-proof. The core of the sensor is a piezoelectric disc, the type normally used as a buzzer. I chose the Murata 7BB-35-3. With 35mm of external diameter, it allows a sensitive area of about 20mm diameter.
Water & vandal-proof keypad uses piezoelectric disc as sensor and buzzer – [Link]
Raspberry Pi has been very popular small computer board. It’s initial layout is quite flexible that allows it to use as standalone computer or embedded device with controllable I/Os. Probably standard Raspberry Pi is more oriented to be small single board computer, where you can connect peripherals like keyboard, mouse, display, Ethernet. The I/O part seemed to be left on a side. Eventually extension boards started to appear to fill the need of functionality like ADC, DAC, more digital I/Os. Eventually you end up stacking stuff on top like Arduino. But we like elegant things don’t we? So Raspberry Pi team has been working on different Raspberry Pi concept – Compute module. This is smaller module which have same BCM2835 processor, same RAM. Instead of SD flash there is a 4Gbyte flash memory. Practically this is it. Module is traced on DDR2 SODIMM sized PCB which actually fits this connector.
Raspberry Pi Compute module – [Link]