DC-DC Converter

Here is a versatile power coupler that connects a device to 5V-19V DC generated from AC mains by a power adaptor. Power adaptors come in different voltage outputs like 5V (for mobile phones), 12V (for external hard drives) and 19V (for laptops). Sometimes the power adaptor may have a voltage rating higher than the required voltage. With the converter circuit given here, the adaptor can be used to power any device at a lower voltage.

For instance, by using a 19V laptop adaptor, you can power a TTL circuit at 5V. There can also be other instances when one needs a 3V or 6V supply. All these and many other intermediate voltages are easily possible with this versatile converter circuit when used together with any off-hand power adaptor.

Circuit diagram :

Fig. 1 shows the circuit of the DC-DC converter. Smooth reduction in the voltage is achieved using the LM317 regulator IC. The complete unit can fit inside a piece of a glue stick tube.

Adjusting variable resistor VR1 gives the desired output voltage. The output voltage is read using a 0-100µA ammeter, whose series resistance R* is chosen such that the maximum desired voltage could be covered. For instance, if full-scale deflection (FSD) current of the meter is 100 µA and you need an output voltage of up to 15V, then R* = 15/0.0001 = 150 kΩ. The desired value of R* is obtained by using 150-kilo-ohm preset VR2.

Use of a variable resistor which also has an on/off switch like the one in old radios is recommended. It will cut off the coupler from the input power supply without having to accomodate an additional switch. Also, use a heat-sink with LM317 to handle the desired amount of power.

Assemble the circuit on a small general-purpose PCB and enclose in a suitable case. Fit the entire PCB inside a glue stick tube as shown in Fig. 2. Affix the female and male connectors on the opposite ends and place the ammeter in between the stick tube. You can directly read the output voltage on the ammeter after due calibration.

Note. You can use a suitable VU meter instead of 0-100µA ammeter and calibrate accordingly.

25W to 35W Inverter

How to build Inverter Circuit 

Here is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 and Q2 (each BC547) form an astable multivibrator that produces 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to pnp Darlington driver stages formed by transistor pairs Q3-Q5 and Q4-Q6 (utilising BC558 and BD140).

The outputs from the drivers are fed to transistors Q7 and Q8 (each 2N3055) connected for push-pull operation. Use suitable heat-sinks for transistors Q5 through Q8. A 230V AC primary to 12V-0-12V, 4.5A secondary transformer (T1) is used. The centre-tapped terminal of the secondary of the transformer is connected to the battery (12V, 7Ah), while the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8, respectively.

When you power the circuit using switch S1, transformer X1 produces 230V AC at its primary terminal. This voltage can be used to heat your soldering iron. Assemble the circuit on a generalpurpose PCB and house in a suitable cabinet. Connect the battery and transformer with suitable current-carrying wires. On the front panel of the box, fit power switch S1 and a 3-pin socket for connecting the soldering iron. Note that the ratings of the battery, transistors T7 and T8, and transformer may vary as these all depend on the load (soldering iron).

Circuit diagram:

Parts:

• P1-P2 = 47K
• R1-R2 = 1K
• R3-R4 = 270R
• R5-R6 = 100R/1W
• R7-R8 = 22R/5W
• C1-C2 = 0.47uF
• Q1-Q2 = BC547
• Q3-Q4 = BC558
• Q5-Q6 = BD140
• Q7-Q8 = 2N3055
• SW1 = On-Off Switch
• T1 = 230V AC Primary 12-0-12V
• 4.5A Secondary Transformer
• B1 = 12V 7Ah 

1.5 - 35 Volt DC Regulated Power Supply

The easy way to power your projects

Here is the circuit diagram of regulated power supply. It is a small power supply that provides a regulated voltage, adjustable between 1.5 and 35 volts at 1 ampere. This circuit is ready to use, you just need to add a suitable transformer. This circuit is thermal overload protected because the current limiter and thermal overload protection are included in the IC.

Picture of the circuit:

1A Regulated Power Supply Circuit Schematic

Circuit diagram:

1A Regulated Power Supply Circuit Diagram

Transformer selection chart:

Transformer selection Guide-Table For Power Supply

Parts:

IC = LM317
P1 = 4.7K
R1 = 120R
C1 = 100nF - 63V
C2 = 1uF - 35V
C3 = 10uF - 35V
C4 = 2200uF - 35V
D1-D4 = 1N4007

Features:

• Just add a suitable transformer (see table)
• Great to power your projects and save money on batteries
• Suitable as an adjustable power supply for experiments
• Control DC motors, low voltage light bulbs, …

Specifications :

• Preset any voltage between 1.5 and 35V
• Very low ripple (80dB rejection)
• Short-circuit, thermal and overload protection
• Max input voltage : 28VAC or 40VDC
• Max dissipation : 15W (with heatsink)
• Dimensions : 52x52mm (2.1” x 2.1”)

Technical Specifications

• Input Voltage = 40Vdc max Transformer
• Output Voltage = 1.5V to 35Vdc
• Output Current = 1.5 Amps max.
• Power Dissipation = 15W max (cooled)

Note:

• It has not to be cooled if used for small powers. 28 Volt AC max is allowed for the input voltage.

USB TO RS232 converter

This project lets you conveniently connect any computer with USB ports directly to a simple, traditional connector  the 9-pin RS-232,It converts the electrical signals from a USB<–>serial TLL convertor to the RS-232 standard. So in a nutshell,it converts a USB port into a standard but basic serial port.

                                                          

 The voltage level adaptor is a MAX3232 from Maxim. This industry-standard part comprises two transmitters and two receivers, ideal for our USB<–>serial convertor, which itself offers the four fundamental signals of an RS-232 standard port, namely TXD (Transmit Data), RTS (Request To Send), RXD (Receive Data) and DTR (Data Terminal Ready).

Simple Logic Probe

This circuit effectively functions as a logic-level indicator or logic probe for TTL circuits. It gives an indication of any of the following four conditions that might be found on a typical digital circuit and thus provides a versatile troubleshooting aid: 1. Line high (logic 1) 2. Line low (logic 0) 3. Line tri-state (high impedance) 4. Line changing between high and low state alternately (pulsating). The logic probe is powered from the power supply of the digital equipment under test. The logic state of the line under test is indicated by two LEDs (LED1 and LED2). If the line being probed is at logic 1 (high) state, LED2 would glow brightly. If the line is at logic 0 (low) state, LED2 would be off. If the line is at tri-state or open then LED2 would be dimly lit (about half of its full brightness). If the line has a pulsating signal or a clock signal, LED1 would flash on and off at a rate of 1 Hz. Thus LED2 gives an indication of static signal states, while LED1 indicates dynamic signal conditions on the line being probed. The various states of LED1 nd LED2 are summarised in Table I. In order to obtain a visible indication of a clock signal presence on LED1, a divider, which comprises two monostable multivibr- ators, is made use of. The monoshots are realised using IC1 (dual timer 556). The output of the first monoshot section (pin 5) is applied to the trigger input (pin 8) of the second timer. Assume a clock frequency of 10 kHz is applied to the probe tip. The falling edge of the clock at pin 6 of IC1 triggers the first monoshot section. The output of the first monoshot stays high for around 0.5 seconds and then goes low. This low going edge triggers the second monoshot section, making its output (pin 9) high for around 0.5 seconds. While pin 9 is high, the first monoshot section is prevented from being retriggered with the help of transistor T1. When pin 9 reverts back to the low state, the first monoshot can be retriggered. This arrangement ensures that LED1 flashes ‘on’ and ‘off’ at a visible rate of around 1 Hz, thus indicating a clock presence on the line under test. The circuit will detect clock frequencies between 1 Hz and 100 kHz, approximately. For any clock frequency within this range, LED1 will flash at a constant rate of 1 Hz. When the probe tip is connected to a line at logic 1, currents flowing through resistors R9 and R10 add up in LED2 and make it glow brightly. When probe tip is connected to a line at logic 0, the voltage at the junction of resistors R9 and R10 is not sufficient to turn on LED2 (hence it remains off). When the probe is not connected any- where or is connected to a tri-stated line, LED2 remains dim because of current flowing through R9 only. The whole circuit can be enclosed in a small plastic tube with LED1 and LED2 exposed. A pin can be used as the probe tip. The usefulness of this logic probe is limited to low frequency digital circuits.

                                   

                                 

Wireless On-Off Switch

Small and simple circuit, Suitable for home appliances

Normally home appliances are controlled by means of switches, sensors, etc. However, physical contact with switches may be dangerous if there is any shorting. The circuit described here requires no physical contact for operating the appliance. You just need to move your hand between the infrared LED (D2) and the phototransistor (Q1). The infrared rays transmitted by D2 is detected by the phototransistor to activate the hidden lock, flush system, hand dryer or else. This circuit is very stable and sensitive compared to other AC appliance control circuits. It is simple, compact and cheap. Current consumption is low in milliamperes. The circuit is built around an IC CA3140, D2, phototransistor and other discrete components.
Circuit Diagram:

Parts:
R1 = 470R
R2 = 100K
R3 = 3.3K
R4 = 10K
D1 = 1N4007
D2 = IR LED
Q1 = L14F1
RL = 5Vdc Relay
IC = CA3140
Q2 = BC548

Circuit Operation:
When regulated 5V is connected to the circuit, D2 emits infrared rays, which are received by phototransistor Q1 if it is properly aligned. The collector of Q1 is connected to non-inverting pin 3 of IC1. Inverting pin 2 of IC1 is connected to voltage-divider preset R4. Using preset R4 you can vary the reference voltage at pin 2, which also affects sensitivity of the phototransistor. Op-amp IC1 amplifies the signal received from the phototransistor. Resistor R3 controls the base current of transistor BC548 (Q2). The high output of IC1 at pin 6 drives transistor Q2 to energies relay RL1 and switch on the appliance, say, hand dryer, through the relay contacts. The working of the circuit is simple. In order to switch on the appliance, you simply interrupt the infrared rays falling on the phototransistor through your hand. During the interruption, the appliance remains on through the relay. When you remove your hand from the infrared beam, the appliance turns off through the relay. Assemble the circuit on any general-purpose PCB. Identify the resistors through colour coding or using the multimeter. Check the polarity and pin configuration of the IC and mount it using base. After soldering the circuit, connect +5V supply to the circuit.

Water Level Indicator

Water Level Indicator 

Description

                 Figure shows the circuit diagram of the ' Water Level Indicator '. Here I have used copper plates and led for making this circuit. Pure water does not conduct but available water already has some ions. Here is the right copper plate has ground potential so when the water reaches the first left copper plate, the low LED will glow. When the water reaches the higher position, the full LED will glow.