Schematic Rise

Thursday, September 11, 2014

Contactless telephone ringer circuit

The contact less telephone ringer schema can produce a ring as well as a visual indication when a call comes.The main advantage is that since there is no direct contact between the phone line and the schema there is no chance for a loading or disturbance in the telephone line.

When the telephone rings 60 Hz AC signal is generated which produces a proportional magnetic field around the telephone lines.These magnetic field will be picked up by the coil L1 due to electromagnetic induction.A proportional voltage is developed across L1 and it will bias transistor Q1 to ON.This results in the conduction of transistors Q2,Q3 andQ4.The buzzer will ring and the LED will glow.The switch S1 acts as an ON/OFF switch.

Notes.

* For L1 make 50 close turns of 28 SWG enameled copper wire on any of the two telephone wires.Connect one end of the coil to base of Q1 and leave other end free.
* If the schema not works by try by changing the end of the L1 connected to base of Q1.
* A 9V transistor radio battery can be used as the power source.
* Assemble the schema on a good quality PCB or common board.
* Use of this type or any other devices other than the allowed telephones and devices with the telephone line may be a law violation in some nations.Check it properly before trying.

Simple Cable Bootstrapping Wiring diagram Schematic

This is a Simple Cable Bootstrapping Circuit Diagram. Bootstrapping or booting refers to a group of metaphors which refer to a self-sustaining process that proceeds without external help. In computer science, bootstrapping is the process of writing a compiler.In this schema Bootstrapping input shield for a follower reduces cable capacitance, leakage, and spurious voltages from cable flexing Instability can be avoided with small capacitor on input.

Simple Cable Bootstrapping Circuit Diagram

Simple LED Torch

A common problem with small torches is the short life-span both of the batteries and the bulb. The average incandescent torch, for instance, consumes around 2 Watts. The LED Torch in Fig. 1 consumes just 24 mW, giving it more than 80 times longer service from 4 AA alkaline batteries (that is, up to one months continuous service). Although the torchs light output is modest, it is nonetheless quite sufficient to illuminate a pathway for walking.

Circuit Diagram :

Fig. 1 : Simple LED Torch Circuit Diagram

The LED Torch is based on a 7555 timer running in astable mode (do not use an ordinary 555). A white LED (Maplin order code NR73) produces 400 mcd light output, which, when focussed, can illuminate objects at 30 metres. Try Conrad Electronic for what appears to be a stronger white LED (order code 15 37 45-11). A convex lens with short focal length is placed in front of the LED to focus the beam. If banding occurs at the beams perimeter, use another very short focal length lens directly in front of the LED to smooth the beam.

If a different supply voltage is preferred, the value of resistor R3 is modified as follows:

9V - 470 Ohm
12V - 560 Ohm

See my "Wind-up Torch" feature article in the October 2000 edition of Everyday Practical Electronics for a completely battery-free go-everywhere torch.

Wednesday, September 10, 2014

Simple Electronic Lock

Simple Electronic Lock Circuit diagram. There are six (or more) push switches. To unlock you must press all the correct ones at the same time, but not press any of the cancel switches. Pressing just one cancel switch will prevent the schema unlocking. When the schema unlocks it actually just turns on an LED for about one second, but it is intended to be adapted to turn on a relay which could be used to switch on another schema. Please Note: This schema just turns on an LED for about one second when the correct switches are pressed. It does not actually lock or unlock anything!

Simple Electronic Lock Circuit diagram :

Simple Electronic Lock Circuit Diagram

Stripboard Layout :

Parts :

resistors: 470, 100k ×2, 1M
capacitors: 0.1μF, 1μF 16V radial
on/off switch
push-switch ×6 (or more)
stripboard 12 rows × 25 holes
red LED
555 timer IC
8-pin DIL socket for IC
battery clip for 9V PP3

A kit for this project is available from RSH Electronics: www.kpsec.freeuk.com

Simple Isolated Converter Wiring diagram Schematic

This the Simple Isolated Converter Circuit Diagram. In this Simple Isolated Converter Circuit Diagram a negative output voltage de-de converter generates a -5 V output at pin A. In order to generate -5 Vat point A, the primary of the transformer must fly back to a diode drop more negative than -5 V. If the transformer has a tightly coupled 1/1 turns ratio, there will be a 5 V plus a diode drop across the secondary.

The 1N5817 rectifies this secondary voltage to generate an isolated 5-V output. The isolated output is not fully regulated since only the -5 V at point A is sensed by the MAX635.

Simple Isolated Converter Circuit Diagram

BA5417 Stereo Power Amplifier

BA5417 is a stereo amplifier IC with lots of excellent features like thermal shut down, standby perform, soft clipping, wide operating voltage range etc. The IC will deliver 5W per channel into 4 ohm loud speakers at 12V DC supply voltage. The BA5417 has glorious sound quality and low THD (total harmonic distortion) around 0.1% at F=1kHz; Pout=0.5W.

Setup and dealing of this stereo power amplifier circuit is somewhat just like the BA5406 based stereo amplifier circuit. C10 and C11 are DC decoupling capacitors that block any DC level present in the input signals. C2 and C6 couples the amplifiers left and right power outputs to the corresponding loud speakers. C1 and C5 are bootstrap capacitors.

Bootstrapping is a method in which a little of the amplifiers is taken and applied to the input. The prime objective of bootstrapping is to enhance the input impedance. Networks R1,C3 and R2,C7 are meant for improving the high frequency stability of the circuit. C4 is the power supply filter capacitor. S1 is the standby switch. C8 is a filter capacitor. R3 and R4 sets the gain of the left and right channels of the amplifier in conjunction with the 39K internal feedback resistors.

VHF field strength meter

This is a simple and low cost wide band VHF field strength meter. The field strength is measured by converting the radio signal to DC and measuring it.

The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This schema is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations).

Notes.

* The schema can be assembled on a general purpose PCB.
* Use a 9V PP3 battery for powering the schema.
* Use a 250uA FSD current meter for M1.Using a lower FSD meter will improve sensitivity.
* The coil L1 can be made by making 6 turns of 20 SWG enameled copper wire on a inch plastic former.
* The antenna can be a telescopic whip antenna.