Schematic Rise

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Saturday, November 8, 2014

Going for Gold Circuit Diagram

The title refers to a popular TV game show where the contestants each have a big button. The game show host asks a question and the first contestant to press their but-ton makes an illuminated indicator light up on their desk. The other contestants’ buttons are automatically inhibited, so that everyone can see who was the first contestant to press their button, and so is allowed to answer the question. The project described here shows how to build a similar sortof refereeing device yourself, using simple resources and without needing a microcontroller, which is pretty rare these days! The basic circuit is for just two contestants, but the modular design means it can easily be expanded.

Circuit diagram :

Going for Gold Circuit Diagram

The diagram shows three buttons: S2 and S3 are the buttons for the two contestants, S1 is the button for the host, which allows them to reset the circuit before each fresh question. The ‘brains’ of the circuit is IC1, a 4013 dual D-type flip-flop, of which only the Set and Reset inputs are used here. This circuit can handle quite a wide supply voltage range, from 3 to 15 V, and so the project can easily be run off a 4.5 V battery pack (the power consumption is minimal).

IC1 is armed by pressing S1 (reset). In this state, the non-inverting outputs (pins 1 and 13) are at 0 and the inverting outputs (pins 12 and 12) are at 1. Hence line A is pulled high by R1, since diodes D2 and D4 are not biased on. If contestant 1 presses button S2, the non-inverting output of flip-flop IC1a goes to logic 1, and LED D1 lights via T1 to indicate that contestant 1 has pressed the but-ton. At the same time, the flip-flop’s invert-ing output goes to logic 0, making diode D2 conduct. Line A is now pulled down to 0, and consequently contestant 2’s button S3 can no longer trigger the second flip-flop. The reverse happens if it is contestant 2 who presses their button S3 first.

The circuit can be extended to 4 or 6 contest-ants (or even more) by adding a second or third (or more) 4013 IC. All you have to do is repeat the circuit (minus R1, R2, and S1) and connect to the A, B, Vdd, and 0 V lines on the right-hand side.

Tuesday, November 4, 2014

Video Switch for Intercom System

Nowadays a lot of intercom units are equipped with video cameras so that you can see as well as hear who is at the door. Unfortunately, the camera lens is perfectly placed to serve as a sort of support point for people during the conversation, with the result that there’s hardly anything left see in the video imagery. One way to solve this problem is to install two cameras on the street side instead only one, preferably some distance apart.

If you display the imagery from the two cameras alternately, then at least half of the time you will be able to see what is happening in front of the door. Thanks to the video switch module described here, which should be installed on the street side not too far away from the two cameras, you need only one monitor inside the house and you don’t need to install any additional video cables.

Video Switch for Intercom System Circuit diagram:

Along with a video switch, the circuit includes a video amplifier that has been used with good results in many other Elektor projects, which allows the brightness and the contrast to be adjusted separately. This amplifier is included because the distance between the street and the house may be rather large, so it is helpful to be able to compensate for cable attenuation in this manner. The switch stage is built around the well known 4060 IC, in which switches IC2a and IC2d alternately pass one of the two signals to the output.

They are driven by switches IC2b and IC2c, which generate control signals that are 180 degrees out of phase. The switching rate for the video signals is determined by a clock signal from an ‘old standby’ 555 IC, which causes the signals to swap every 2 seconds with the speciﬁed com ponent values.

Naturally, this circuit can also used in many other situations, such as where two cameras are needed for surveillance but only one video cable is available.

Monday, November 3, 2014

Universal Tester for 3 pin Devices

Most 3-terminal active components can be tested statically using just an ohmmeter. But when you have a lot of these devices to test, the procedure soon becomes boring. That’s where the idea came from to combine fast, easy testing for these types of device into a single instrument.

The unit described here enables you to test NPN and PNP bipolar transistors, N-or Pchannel FETs or MOSFETs, UJTs, triacs, and thyristors. Regardless of the type of device, the tests are non-destructive. Universal connectors allow testing of all package types, including SMDs (up to a point). The unit lets you change from one type of device to another in a trice. It avoids using a multi-pole switch, as they’re too expensive and hard to ﬁnd.

Universal Tester for 3-pin Devices Circuit diagram:

Here’s how to build a versatile instrument at a ridiculously low cost. IC1 is a 4066 quad CMOS switch which will let us switch between bipolar transistors and FETs. LEDs D1–D4 tell us about the condition of the test device, when we press the ‘Test’ button. The 4066 can only handle a few milliamps, not enough for the other component types to be tested, hence the reason for using relay RE1. This 12 V relay offers two NO contacts. The ﬁrst applies power to the UJT test circuit, the second applies it to the triac and thyristor test circuit.

Extensive testing has shown that the best way to test UJT transistors is to do so dynamically, with the help of a relaxation oscillator. Net-work R11/C1 sets the oscillator frequency to around 2 Hz. On pin B1 of the UJT we find a nice sawtooth, which is not of much interest to us here. However, pin B2 gives good but very short pulses. IC2, wired as a monostable, lengthens these pulses so they can be clearly seen via LED D5.

The relay’s second pole is going to drive the thyristor’ sortriac’s trigger pin. The value of R18 is a good compromise with respect to the varying trigger currents for this type of device. Resistor R17 is important, as the hold-ing current must be high enough for a triac; 250 mA is a good compromise. LED D6 tells you if the device is in good condition or not; but watch out, the test result must be con-ﬁrmed by brieﬂy cutting the power in order to reset the triac.

On the web page for this article [1] you’ll ﬁnd the author’s CAD ﬁles (PCB layout and front panel) along with some photos of his project. On the prototype, the LEDs and the ‘Test’ button were wired onto the copper side of the PCB. The six female connectors for the devices being tested were salvaged, but there are lots of models available on the market (the pitch is standard). The test cable crocodile clips must be as small as possible for testing SMD devices.

Wednesday, October 15, 2014

Under voltage Indicator for Battery Equipment Circuit Diagram

This is the simple Under voltage Indicator for Battery Equipment Circuit Diagram. Due to the low duty cycle of flashing LED, the average current drain is 1 mA or less. The NE555 will trigger the LED on when the monitored voltage falls to 12 volts.The ratio of Rl to R2 only needs to he changed if it is desired to change the voltage point at which the LED is triggered.

Under voltage Indicator for Battery Equipment Circuit Diagram

Thursday, September 4, 2014

How to Reuse Old Cell Battery for LED lighting

Normally cell batteries have a shelf life of 2 to 5 years under normal use. After that time we have to replace them. Nowadays there replacement batteries which are cheap, but these batteries last for much less cost only months. An easy solution is to use batteries in a schema that requires less current, we can use them for lighting LEDs.

How to Reuse Old Cell Battery for LED lighting

Tuesday, September 2, 2014

Extension for LiPo Charger Wiring diagram Schematic

Extension for LiPo Charger Project Image

The ‘Simple LiPo Charger’ published in Elektor Electronics April 2005 is a small and handy schema that allows you to quickly charge two or three LiPo cells. Especially in the model construction world are LiPo batteries used a lot these days, particularly model aeroplanes.

It is usual to use a series connection of three cells with these models. Since working with these model aeroplanes usually happens in the field, it would be nice if the batteries could be charged from a car battery.

We therefore designed a voltage converter for the LiPo charger concerned, which makes it possible to charge three cells in series. The voltage per cell increases while charging to a value of about 4.2 V, which gives a total voltage of 12.6 V. The converter, therefore, raises the 12-V voltage from the car battery to 16.5 V, from which the LiPo charger can be powered.

Extension for LiPo Charger Circuit Diagram

Extension-for-LiPo-Charger-Circuit-Diagram

A step-up controller type MAX1771 in combination with an external FET carries out the voltage conversion. The IC operates at a moderately high switching frequency of up to 300 kHz, which means that quite a small coil can be used.

Because the IC uses pulse frequency modulation (PFM) it combines the advantages of pulse width modulation (high efficiency at high load) with very low internal current consumption (110µA).

The IC is configured here in the so-called non-bootstrapped mode, which means that it is powered from the input voltage (12 V). The output voltage is adjusted with voltage divider R2/R3. This can be set to any required value, provided that the output voltage is greater than the input voltage.

Extension for LiPo Charger PCB Layout

Finally, sense resistor R1 determines the maximum output current that the schema can deliver. With the 25 mΩvalue as indicated, this is 2.5 A.

COMPONENTS LIST:
Resistors:
R1 = 25mΩ(e.g., Digikey # 2FR025-ND)
R2 = 100kΩ
R3 = 10kΩ
Capacitors:
C1,C4,C8 = 100nF
C2,C3 = 47µF 25V radial
C5,C7 = 100µF 25V radial
C6 = 100pF
Semiconductors:
D1 = 31DQ05 (e.g., Digikey #31DQ05-ND)
IC1 = MAX1771-CPA (e.g., Digikey #MAX1771EPA-ND)
T1 = IRFU3708 (e.g., Digikey #IRFU3708-ND)
Miscellaneous:
K1,K2 = 2-way PCB terminal block,lead pitch 5mm
L1 = 47µH high current suppressor
coil, (e.g, Digikey # M9889-ND)
PCB.,ref. 054012-1 from The PCBShop

Author : Unknown - Copyright : Elektor

Friday, August 22, 2014

Simple 4 Transistor Amplifier for Small Speakers

The schema above shows a 4-transistor utility amplifier suitable for a variety of projects including receivers, intercoms, microphones, telephone pick-up coils, and general audio monitoring. The amplifier has a power isolation schema and bandwidth limiting to reduce oscillations and "motorboating". The values are not particularly critical and modest deviations from the indicated values will not significantly degrade the performance.

Three cell battery packs giving about 4.5 volts are recommended for most transformerless audio amplifiers driving small 8 ohm speakers. The battery life will be considerably longer than a 9 volt rectangular battery and the cell resistance will remain lower over the life of the battery resulting in less distortion and stability problems.

4 Transistor Amplifier for Small Speakers Circuit Diagram

The amplifier may be modified to work with a 9 volt battery if desired by moving the output transistors bias point. Lowering the 33k resistor connected from the second transistors base to ground to about 10k will move the voltage on the output electrolytic capacitor to about 1/2 the supply voltage.

This bias change gives more signal swing before clipping occurs and this change is not necessary if the volume is adequate. As before, the two 4.7 ohm resistors may be replaced with a single 10 ohm resistor in series with either emitter.

Monday, August 18, 2014

Build a Bipolar Power supply for Battery instruments

How to Build a Bipolar Power supply for Battery instruments. A bipolar power supply overcomes those limitations. Most importantly, it can provide both positive and negative voltages from a single pair of terminals. There are no relays to switch polarity, so a bipolar supply can move smoothly from positive, through zero, to negative voltages.

Bipolar Power supply for Battery instruments Circuit Diagram

It also regulates zero volts or other very small voltages. In this Bipolar Power supply for Battery instruments schema diagram to generate regulated Â± 5-V supplies from a pair of dry batteries, the schema of Fig. 1 is commonly used. In order to give protection from inadvertent reverse connection of a battery, a diode in series with each battery would produce an unacceptable voltage drop.

The more effective approach is to fit diodes Dl and D2 as shown in Fig. 2, in parallel with each battery. When the supply is switched off, there is the risk of a reverse bias being applied across the regulators, if there is significant inductance or capacitance in the load schema. Diodes across the regulators prevent damage. When the power supply is switched on, the two switches do not act in unison.

There is a probability that one or the other regulators will be latched hard off by the other. To prevent this, D3 and D4 are Zener diodes so that Â± 5-V rails are pulled up by the batteries until the regulators establish the correct levels.

Saturday, August 16, 2014

Brightness Control for small Lamps

This device was designed on request, to control the light intensity of four filament lamps (i.e. a ring illuminator) for close-up pictures with a digital camera, powered by two AA or AAA batteries. Obviously it can be used in other ways, at anyones will.
IC1 generates a 150Hz squarewave having a variable duty-cycle. When the cursor of P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow. Lamp LP1, driven by Q1, is off as the voltage across its leads is too low. When the cursor of P1 is rotated towards R2, the output pulses increase in width, reaching their maximum amplitude when the potentiometer is rotated fully clockwise. In this way the lamp reaches its full brightness.

LP1 could be one or more 1.5V bulbs wired in parallel. Maximum total output current allowed is about 1A.
R2 limits the output voltage, measured across LP1 leads, to 1.5V. Its actual value is dependent on the total current drawn by the bulb(s) and should be set at full load in order to obtain about 1.5V across the bulb(s) leads when P1 is rotated fully clockwise.

Parts:
P1 470K Linear Potentiometer
R1 10K 1/4W Resistor
R2 47K 1/4W Resistor (See Notes)
R3 1K5 1/4W Resistor
C1 22nF 63V Polyester Capacitor
C2 100µF 25V Electrolytic Capacitor
D1,D2 1N4148 75V 150mA Diodes
IC1 7555 or TS555CN CMos Timer IC
Q1 BD681 100V 4A NPN Darlington Transistor
LP1 1.5V 200mA Bulb (See Notes)
SW1 SPST Switch
B1 3V (Two 1.5V AA or AAA cells in series, etc.)