Today, although the wireless technology grows very fast, the long distance funicular communication still keeps its popularity. The reason is obvious that cost and complexity is high at the wireless communication.

RS232 is one of the most used, easy to develop and easy to apply communication protocol. We generally encounter to this standard at the MCU applications. But it has some restrictions. It allows us to use maximum 15 meters cable. Good wiring, low baud rates and less noisy mediums may allow us to exceed this limit a little more. The main problem here , when the distance increases, the noise at the common ground line also increases. Another issue, RS232 allows only two devices to communicate reciprocally. More than two devices can not communicate at this line and we need another solution for this situation.

RS485 is the standard that solves this problems. The main difference is,  RS485 transfers the data depending on the potential difference between the two communication wires. The polarity defines the logic state of the signal. You can transfer data up to 1220 meters far away and with a rate up to 10 Mbs. 32 devices can join the RS485 network.

Description

This is a two part infrared remote controller circuit that consists of a transmitter and a receiver circuit pair. When you push the button on the 9V supplied transmitter circuit, a signal at 38kHz frequency is applied on the Infrared (IR) LED. As a result of the current passing through the IR LED, it illuminates the surround  with infrared light. By using the 1k potentiometer, oscillator frequency should be adjusted to 38kHz to operate the circuit properly.

The illuminated infrared light is detected by the IR receiver module. Generally IR modules has three pins and in our project we used the product of Telefunken, TK19 module. Instead of TK19, as an option you can use the SFH506 which is a product of Siemens or any other module for this purpose.
 

When the IR light touches the receiver, the third pin of the module sees logic-0 (low). Other case it is in the logic-1(high) position. So controlling the third pin gives us the information whether the button on the transmitter is pushed or not.

The J-K type flip flop in the receiver circuit controls the relay. When the button is pushed, relay gets in the position closed which was in open position before. So the device gets connected to the mains and starts operating. After second push, relay gets in position open and cuts the device energy...

Description

This circuit is a fan controller which is using the pulse width modulation (PWM) method. It is tiny (33.78mm x 54.76mm) and easy to build. Functions of the circuit parts are listed below;

VR1: 10 K Variable resistor adjusts the fan speed.

R9:  This sets the minimum speed. With the 10k pot, a 1k resistor will give 0–100% control which is OK for model motors or lighting, 10k will give around 5v–12v range, more suitable for cooling fans.

C2: This is the timing capacitor, and with the 47k timing resistor R1 and wave amplitude control resistors R2 (22k) & R3 (10k) gives a PWM frequency of around 117Hz according to the formula

Frequency = R2 / (4 x R3 x R1 x C1)

Q1: For load currents up to about 600mA a 2N2222A NPN transistor is recommended. It comes in a TO-18 metal can.

For higher loads go for a darlington power transistor such as the TIP120, 121 or 122, rated to 5A, or a power mosfet. The IRF530 is easy to find, not expensive, and can carry up to 14A. Providing you take the usual precautions for handling CMOS, static electricity is not going to zap it. Most n-channel MOSFETs will do, look for a low RDS(on) and adequate current-handling ability. Both darlingtons and mosfets are in the TO-220 case.

Using the 2N2222A bipolar transistor you might lose 200-400mV from the 12v supply to the fan, double that for one of the darlington types; with the IRF530 I measured the loss at only 40mV with a 200mA fan.

Check the transistor or mosfet pin-outs, base or gate to R9, emitter or source to ground, collector or drain to the fan negative. A heatsink is not necessary at moderate loads. 

D1: The diode prevents back-emf from inductive loads such as brushed motors from damaging the switching transistor. With "brushless" computer fan motors it's not necessary to fit this diode across the load, as they have any needed protection already in-fan.

Click here to download the schematic, PCB and layout files

This circuit is a relay driver that is based on a PIC16F84A microcontroller. The board includes four relays so this lets us to control four distinct electrical devices. The controlled device may be a heater, a lamp, a computer or a motor. To use this board in the industrial area, the supply part is designed more attentively. To minimise the effects of the ac line noises, a 1:1 line filter transformer is used.

The transformer is a 220V to 12V, 50Hz and 3.6VA PCB type transformer. The model seen in the photo is HRDiemen E3814056. Since it is encapsulated, the transformer is isolated from the external effects.

A 250V 400mA glass fuse is used to protect the circuit from damage due to excessive current.

A high power device which is connected to the same line may form unwanted high amplitude signals while turning on and off. To bypass this signal effects, a variable resistor (varistor) which has a 20mm diameter is paralelly connected to the input.

Description

This project is based on ISD2560P IC which allows you to record 60 seconds voice and then playback the recorded voice with very high quality. As shown in the schematic, the input source is an electret microphone. If a dynamic microphone is used,  R2,R3,R4 resistors and C3,C5,C7 capacitors will be omitted and microphone will be connected to the 17 and 18 numbered pins directly. Since it has better frequency response, we choose electret microphone in this project.

Controlling the circuit is very simple. Sw1 switches between record and playback modes. Push button B1 is used for start and pause functions. B2 stops the during process.

To record voice, first move Sw1 to the record position and then push B1 once. IC will start recording and during this process red LED will bright. One push to B1 pauses and second push continues recording. You can record 60 seconds by this way. To stop recording push B2.

To listen the voice recorded before, move Sw1 to playback position then push B1. During the playback process red LED will bright again. One push to B1 pauses and second push continues playing. To stop playback push B2...

Description

When I set out to design this amplifier, my aim was to create a product most suitable for the reproduction of complex music and speech signals. Although I placed high emphasis on electrical characteristics, the single most important requirement is achieving an audibly superior sound, vivid spatial imaging and superb tonal clarity.

Although the average listening level is normally less than 10 watts, my design approach was to create an amplifier with ample reserve power, but biasing it for class A at average listening levels reducing cross-over distortion to extremely low levels.

There is not one capacitor in the signal path, improved the accuracy of the tonal characteristics of instruments and voices significantly.
The RAS 300 has almost zero phase distortion far beyond the audio range resulting in perfect resolution and totally un-coloured sound.

Amplifier Specification:
Maximum Output: 240 watts rms into 8 Ohms, 380 watts rms into 4 Ohms
Audio Frequency Linearity: 20 Hz - 20 kHz (+0, -0.2 dB)
Closed Loop Gain: 32 dB
Hum and Noise: -90 dB (input short circuit)
Output Offset Voltage: Less than 13 mV (input short circuit)
Phase Linearity: Less than 13 0 (10 Hz - 20 kHz)
Harmonic Distortion: Less than 0.007% at rated power
IM Distortion: Less than .009% at maximum power