Electronics-Lab.com Blog

TrH Meter is a DIY microcontroller-based indoor thermometer plus hygrometer that displays temperature (F/C) and relative humidity on 4 seven segment LED displays which adjust their brightness level according to the surrounding illumination. The displays are 1 inch big, emits bright yellow color, and are readable from more than 50 ft away. It consists of a closed loop system that continuously assesses ambient light condition using an inexpensive light-dependent resistor (LDR) and uses that information to adjust the brightness of the display. The DHT11 sensor is used to measure temperature and relative humidity. The microcontroller used in this project is PIC16F688, and it runs at 4 MHz internal clock. A separate display driver chip (MAX7219) is used to control and refresh the display data on the seven segment LEDs. A 3-position slide switch controls power ON/OFF and Fahrenheit (F) or Celsius (C) scale select for temperature display. You can now preorder the project kit for a discounted price of $25 on Tindie. You will receive a preprogrammed PIC16F688 microcontroller in the kit.

TrH Meter project kit is now available for preorder on Tindie - [Link]

This project is about building a microcontroller-based digital room thermometer plus hygrometer that displays temperature and relative humidity on 4 large (1 inch) seven segment LED displays which adjust their brightness level according to the surrounding illumination. It consists of a closed loop system that continuously assesses ambient light condition using an inexpensive light-dependent resistor (LDR) and uses that information to adjust the brightness of the display. An inexpensive DHT11 sensor is used to measure temperature and relative humidity. The microcontroller used in this project is PIC16F688, and it runs at 4 MHz clock generated from its internal source. A separate display driver chip (MAX7219) is used to control and refresh the display data on the seven segment LEDs.

TrH Meter: A DIY indoor thermometer plus hygrometer with adaptive brightness - [Link]

Raj from Embedded Lab shows in his latest tutorial guide how to implement adaptive brightness control to seven segment LED displays for optimum readability in all illumination conditions. The technique has been demonstrated by constructing a temperature and humidity meter that adapts the brightness of the seven segment LED displays to the surrounding lighting conditions.The project uses a general purpose LDR to sense the surrounding illumination and MAX7219 to drive the LED display.

How to implement auto-brightness adjustment to seven segment LED displays – [Link]

embedded-lab.com writes:

Measurement of light intensity is a prime necessity in several occasions.  The diversity of such needs make their way to various branches of physics and engineering as well as in media. For instance, in engineering, such kinds of measurements are needed to design optimum lighting conditions of a room. In photography, light intensity measurements ensure good quality pictures by determining the right exposure. Wiring a phototransistor or a light-dependent-resistor (LDR) with an analogue LED voltmeter chip like the LM3914 or even to a microcontroller and displaying the ADC values is a pretty simple technique of measuring light intensity. The bad part of this technique is that these simple and amateur-level devices can only measure relative intensity of light and are unable to provide measurements on an absolute scale. However, with a precise knowledge of the transfer characteristic (resistance vs light intensity) of the LDR it is possible to relate the LDR output to the intensity of light in standard unit. In case the LDR characteristic is unknown or unreliable, you can still calibrate the sensor output by using a variable light source and an external reference photometer. This project is about a microcontroller based light intensity meter where an LDR light sensor is calibrated against an external photometer to obtain the intensity of incoming light in the unit of lux. The lux is the SI unitm of illuminance and luminous emittance, and measures lumens per square meter (lm/m²). The microcontroller used in this project is ATMega8L and its firmware is written using mikroElektronika’s MikroC Pro for AVR compiler.

Building a digital light meter with a calibrated LDR - [Link]

Chris The Carpenter has put together possibly the most complete robot module for the Propeller Platform. Called the 444AVXB, he writes… [via]

Let’s start with the name, 444-AVXB stands for:
4 Amps (2 amps x 2 motors) via a L298 motor driver
4 ADC’s (Analog inputs) via a MCP3204 chip
4 Servos with connections to power and with current-limiting resistors on the signal wires
Audio-out (non-amplified)
Video-out via a standard RCA jack
Connections for an X-bee
Connections for a BlueSmirf Bluetooth unit

he 444-AVXB was designed with the robot hobbyist in mind. Connections are available for just about every “standard” thing you would find on a small to medium-sized robot. A hefty motor driver handles decent-sized motors with nice screw terminals for both power and motor connections. (4) 3-pin connections are provided for servos which can be powered by either external power or on-board power. An ADC chip allows for 4 analog inputs to be read, great for analog sensors, pots, LDR’s etc.

Video-out takes advantage of the awesome video capability of the prop and can be connected to any TV with a “video-in” and/or many of the cheapie 7” LCD screens (found on Ebay). Audio is just that, audio out with the circuit being the same as can be found on many other propeller products. Pin 15 has been brought forward as well for a Ping))) sonar unit. Finally, there is room and connections for EITHER an X-bee or Bluetooth module. All unused pins are accessible via female headers.

A Robot Module with Everything - [Link]

Fileark writes:

Photocells, (LDR) Light Dependent Resistor, Photo Resistor, Cadium Sulfide Cell (CdS), all of these names refer to the same thing. Photo Cells are semiconductors that are also resistors that change their resistance depending on the amount of light.

What is a Photo Resistor – [Link]

This project is a solar tracker based on light depended resistors, relays and opamps. Check the installation of circuit solar tracker to diseqc motor.

Relay Solar Tracker - [Link]

An optocoupler volume control! What makes this one neat is that optocouplers are used in the circuit. The optocoupler consists of an LED and Light Dependent Resistor (photocell) in a sealed unit. So by varying the intensity of the LED, you can adjust volume. Also, the volume control has no “contact points” in the signal path. So forget about those scratchy potentiometers and get rid of the contact cleaner. The project as shown is 2 channels, but one could easily scale this one up to control multiple channels which could be useful for a DIY home theater.

DIY Lightspeed Passive Attenuator - [Link]

Dark Sensitive Switch is a simple project which operates a relay when the light falling on the LDR goes below a set point.

• Input – 12 V @ 55 mA
• Relay output – NC-C-NO
• Onboard preset to set the level
• Power-On LED indicator
• Relay On LED indicator
• Power Battery Terminal (PBT) for easy relay output connection
• Four mounting holes of 3.2 mm each
• PCB dimensions 44 mm x 49 mm

Dark Sensitive Switch - [Link]

Have you ever asked yourself how do hundreds and thousands of fireflies are able to synchronize themselves? How does it work, that they are able to blink all together without having a kind of boss firefly? This instructable gives a solution how to build yout own LED firefly and shows how this synchronization can be achieved. Electronic fireflies are based on ATtiny13, LDR (Light Dependent Resistor) and green Led

Synchronizing LED Fireflies - [Link]