Feed: Cool Electronic Circuits - AggScore: 55.3

Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable!) package, indeed.

Although voltage regulator LM317 is capable of delivering up to 37V, the DC power supply output circuit here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink.

Make sure that the input voltage is at least a couple of Volts higher than the desired output. It's ok to use a trimpot if you're building a fixed-voltage supply.

Problems:
Follow all the safety precautions when working with mains voltage. Insulate all connections on the transformer.

Possible uses:
Variable workbench power supply, fixed-voltage supply. Just about any possible application when no more than 1.5A is necessary.

This DC-DC Converter can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won't drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses.

Parts List
R1-R4,R7-R8 100K 1/4W Resistor
R5 470 Ohm 1/2W Resistor
R6 10K Linear Pot
C1 0.01uF Mylar Capacitor
C2 0.1uF Ceramic Disc Capacitor
C3 470uF 63V Electrolytic Capacitor
D1 1N4004 Rectifier Diode
D2 BY229-400 Fast Recovery Diode See Notes
Q1 BC337 NPN Power Transistor
U1 LM358 Dual Op Amp IC
L1 See Notes
MISC Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1

DC- DC Converter Notes
1. R6 sets the output voltage. This can be calculated by Vout = 12 x (R8/(R8+R7)) x (R6B/R6A).
2. L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H).
3. D2 can be any fast recovery diode rated at greater then 100V at 5A. It is very important that the diode be fast recovery and not a standard rectifier.
4. Q1 will need a heatsink.

Source : 12V To 24V DC-DC Converter Circuit

NiCAD batteries have a capacity specification called milliamp-hours. This value called "C" is a measure of how much total current they can provide in one hour. Milliamp-hours is another way to express the energy contained in the battery. To recharge a NiCAD battery conservatively, it is common practice to pump a current of 0.1 C into the anode or positive terminal for about 12 hours. Therefore, if you had a D-size NiCAD with a capacity of 4000mAh, you would want to charge it at 400mA for about 12 hours. Another advantage of this charging technique is that it is gentle on batteries and doesn't cause them to lose capacity as quickly as the fast charge techniques.

The output current of this battery charger circuit  is controlled by the summation of the bandgap reference diode and the base-emitter junction of the PNP transistor. The PNP transistor provides negative feedback to the gate of the MOSFET. As noted in the schematic, the batteries being charged can have a total of 12V which is equivalent to about 8 NiCAD's in series. The output current is determined by the value of R1 which is determined by:


The power dissipation of R1 will equal:


Be sure to provide pleanty of heatsink for Q1 and choose an appropriately sized resistor for R1. The following table summarizes some of the resistor current combinations that are possible:
Iout Resistor Value Resistor Power
Source: Battery Charger

The laptop power supply described here plugs into a car cigarette lighter socket and produces a 19V nominal output voltage adjustable by + - 0.5V. The input voltage range is from 9.2V to 15V and the output voltage shows good regulation even with large fluctuations of the input voltage. The output can supply 5A continuosly with brief excursions up to 10A.

The power semiconductor heatsinks of this laptop power supply are dimensioned fo 5A continuous so extended operation up to 10A will increase dissipation in the adapter and in extreme cases will cause the input fuse to complain.

Laptop PSU Adaptor Parts List
Resistors:
R1 = 5k6
R2 = 51k (51k1)
R3 = 9k1 (9k1)
R4 = 1M
R5 = 4k7
R6,R8 = 15k
R7 = 27k
R9,R10 = 6,8
R11 = 10k
R12 = 100
P1 = 5k preset
Capacitors:
C1-C4 = 3300µF 16V, radial, low ESR, diam. 12.5 mm, e.g. Panasonic EEUFC1C332 (Farnell)
C5,C10 = 1µF MKT, lead pitch 5mm or 7.5mm (larger version preferred)
C12 = 1µF MKT, lead pitch 5 mm
C6-C9 = 2200µF 25V radial, low ESR, diam. 12.5mm, e.g., EEUFC1E222 (Farnell)
C11 = 22nF, lead pitch 5mm
C13 = 2nF2, lead pitch 5mm
C14,C15 = 100nF ceramic, lead pitch 5mm
C16 = 10µF 63V radial
Inductors:
L1 = 56µH, 21 turns 10 x 0.5 mm ECW, parallel
1 x ETD 29 coil forner, vertical mounting, Epcos B66359X1014T1 (Schuricht # 331622)
2 x ETD 29 clamp, Epcos B66359-A2000 (Schuricht # 333862)
2 x ETD 29 core half, material # N67, air gap 0.5mm, Epcos B66358-G500-X167 (Schuricht # 333840)
Semiconductors:
D1 = MBR1645 (International Rectifier) (e.g. Reichelt, Segor)
T1 = IRL2505 (International Rectifier) TO-220AB case, (e.g., RS Components)
T2 = BD139
T3 = BD140
IC1 = UC3843N (Texas Instruments) (e.g. Reichelt, Segor)
Miscellaneous:
K1-K4 = 2-way spade terminal, vertical, PCB mount
F1 = fuse, 10A/T (slow) 6.3 x 32 mm (¼ x 1¼ inch) + 2 fuse holders for 6.3 mm diameter and PCB mounting
2 x heatsink type SK104-STC (or STS) TO220 38.1mm, 11K/W (Fischer Electronic) Isolating washers for T1 and D1 (TO-220AB) + isolating bushes
PCB

Laptop PSU Adaptor PCB-Layout


Source: Laptop Power Supply Adaptor 95W

The DC to AC inverters are widely used in rural electrification the require AC power which includes solar home systems, health clinics, and community centers. Power Converter can also be used for other photovoltaic systems that convert light energy into electricity such as weekend homes and remote cabins, boats and caravans, and small telecom photovoltaic systems.

Power Converter Circuit Explanation
The power converter circuit is constituted by the oscillator, round the IC1, one divider IC2, one unstable multivibrator IC3, which give in the output symmetrical square signal of frequency 50HZ, follow a buffer stage with Fet Q1-2, the drive stage Q3-4 and the power stage Q4-5, the power transistors Q5-6, should they are placed in heatsink.




The diodes Zener D2-3, protect the power transistors from voltage peaks, that are produced by the transformer T1. Transformer T1 are a simple power transformer, with intermediate reception, which is connected in the contacts of CO1. For the use that him we want, the T1, is placed in reverse, with secondary convolution it is used as primary, with the intermediate reception she is connected in the positive point of battery 12V and the two other contacts are connected in the emitters of Q5-6, that are connected in the potential of ground alternately, depending on the rythm that determine outputs 10 and the 11 from IC3.

With this way while in being primary flow AC current, in secondary is created 220V AC square voltage. The use of crystalic oscillator ensures very good reference frequency 50HZ, and use a simple crystal (CR1). For bigger precision, parallel with the C1, exist a variable capacitor Cx, that ensure the regulation of frequency, so that we take in point P1, frequency 204.8 KHZ.

It's obvious that the output voltage in void of load is bigger than the voltage with load. Also the output voltage depend from the output voltage of battery. Thus for battery voltage 14V, the output voltage is increased at 10%, compared to the battery voltage 12V. If the converter work in load power 40 until 60W, then it can be used transformer 2X9V. Various prices of output, for battery voltage 12V and transformer 2X10V,

Power Converter Parts List
Resistor
R1=10Mohms
R2=100ohms
R3=1.2Kohms
R4=560Kohms
R5-6=2.2Kohms
R7-8=56 ohms 5W
Capacitor
CX=22pF trimmed capacitor
C1-2=22pF ceramic
C3=8.2nF 100V MKT C4=10uF 16V
C5=47uF 16V
C6=470nF 400V
Diode
D1=5V6 0.4W
D2-3=47V 1W
Transistor
Q1-2=BS170
Q3-4=BD139
Q5-6=BD249
Integrated Circuit
IC1=4060
IC2=4013
IC3=4047
Crystal
CR1=3.2768 MHZ crystal
Transformer-Fuse
T1=220Vac/2X10V 2X2.2A
F1=5A Fuse
F2=0.25A Fuse
Inductor
L1=1H smoothing choke

Power Converter Printed Circuit Board Layout


Source: 12VDC to 220VAC_Converter

The 10K resistor (*) is only required if you want the receiver to mute (squelch) under no-signal conditions. You could add a 100K in series with this resistor to get an adjustable squelch. This circuit will JUST drive a crystal earphone or high impedance headphones directly, but an output isolating capacitor (100nF) is needed for any other device. L1 is 6 turns No 18 SWG enamelled wire on a 5mm former, but you may have to play with the values a bit. I used a coil fabricated on the PCB itself, tuned with a trimmer capacitor.


All the other components are just a bunch of capacitors which are fitted to the board at the other side of the chip, just to make it look a bit prettier.


As you can see, this receiver is VERY sensitive, small and seems to work very well indeed. It is in fact a full superhet receiver with a very low RC tuned IF. The Image signal is rejected by the action of the AFC which functions to push it away. With suitable antennas and terrain, with this receiver you could easily get the full 500 meters from the FM wireless microphone v5. I am offering this receiver in kit form, including solder, antenna wire etc. All you will need to provide is the battery, tools and soldering iron. Here is the kit version fully assembled.



The total size is 45mm x 48mm. If there is any interest in the kit then I may even add an AF amplifier kit so that you can make a full bedside/table radio.

Source: TDA7000 RX

This High Power FM Wireless Microphone has a better frequency stability, over 1 Km range and is good on microphone sensitivity. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little.


Construction is quite simple. L1 is 3.25 turns in spiral form and is an integral part of the PCB foil pattern. The two BC547 transistors can be replaced with (almost) any small-signal NPN transistor, such as the 2N2222. The final stage is a BC557 PNP general purpose device. If you use different devices then you should select the 1M0 resistor for 5-volts DC at the collector of the the first transistor. Select the 47K resistor for 3 - 4 volts on the collector of the third transistor. Here is the V5 component overlay drawing. Note that there is a modification:


The PCB is 50mm x 25mm, a little larger than the first version but there are three stages instead of just the one. The first prototype is shown above, beside the battery powering it. The output power is about +10dBm which is about 10dB more than the first FM Wireless Microphone. This would theoretically give it 3.12 times the range (1.6Km) but I have only tested it using a handheld receiver with the TX laying on the bench indoors. But I got a comfortable 700 meters (and a few funny looks from our neighbours).


Above you can see the addition of a "gimmick" capacitor added across the 12p tuning capacitor to lower the frequency of the transmitter. Make the capacitor by twisting two lengths of single core insulated hook-up wire, about 2cm long. This will reduce the frequency to the bottom end of the band. Cut short the capacitor to increase the frequency to the desired final frequency. If you cut it a few KHz too high then just twist the gimmick a little tighter.


The PCB foil pattern and layout will be placed in the download section of my homepages. Have fun and please be aware that the higher power of this project may render it ILLEGAL in your own country. I can accept no responsibility and it is up to you to check that you may legally use it. I will accept NO complaints from any country/state correctional facility.

Source: High Power FM Mic

The level power output of an FM transmitter is indicated by the illumination of a LED and the voltage reading on the multimeter gives a further indication of the output.


A digital multimeter may be used but the presence of RF may produce a false reading. Likewise, the radiated energy may upset some analogue meters and you may get full scale deflection on the 15v range as well as the 250v range! But the LED won't lie. It will accurately indicate the RF and you can see the change in brightness as you adjust the coils in the output stage. Some of the cheapest and simplest multimeters will give the best results as they have a low sensitivity and the radiated RF energy will not induce a reading. Even a damaged multimeter can be used, provided the 10v or 15v DC scale is operating.

The reading is not calibrated and does not represent milliwatts output. It is only a visual indication.
We have designed over 10 FM transmitters for inclusion in the pages of this e-magazine and each one has different features and characteristics. Some are designed for 3v operation, some are for 9v operation, some are stable for hand-held situations and others are designed for high output. The illumination of the LED will range from barely visible to very bright.

LED Power Meter Parts
1 - 470R
1 - 100p ceramic
1 - 100n ceramic
2 - 1N 4148 diodes
1 - 5mm Red LED
1 - 2in (5cm) hook-up wire
2 - paper clips
No PC board required

Read more: LED Power Meter

IC 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 Vdc.

That time the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the IC 555 timer circuit to produce an approximate one second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with most capacitor or most resistor at pins 2 and 6 of the IC 555 timer

Source: 9 Sec Timer with LED indication and Control Relay Circuit

Power Supply Schematic


Power Supply circuit above shows the circuit layout for this project. A centre tapped transformer (TR1) is used with two 12V secondary windings with its centre tap tied to ground. This allows positive and negative voltages to be generated with respect to the central ground. Rectification follows based upon the bridge rectifier (BR1) and smoothing capacitors (C1, C2, C4 and C5).

Two linear regulators are used, an LM317 on the positive side and an LM337 on the negative side. These regulators keep the supply voltage constant for a varying load up to a load current of around 1A. The voltage adjustment is achieved through potentiometers RV1 and RV2 in the positive side of the circuit. The clever part of this circuit comes from the mirroring of the positive voltage adjustment to the negative side via the op-amp U2 to give the circuit its tracking nature.

The op-amp U2 has its positive input tied to ground via a 4K7 resistor. This means that, providing there is negative feedback around the op-amp, the op-amp will endeavour to make its negative input also at ground or 0V. The negative feedback is arranged by the output of the op-amp U2 driving the Adjust pin of the negative regulator U3 and by resistors R3 and R4. The op-amp U2 sets the voltage on the adjust pin of U3 such that the voltage at its negative input is 0V. Also as R3 and R4 are equal, the positive and negative regulated voltages must then be equal in magnitude.

An analogue meter is driven from the positive side to give an indication of the voltage setting. Two switches are used to allow the positive and negative supplies to be turned on/off independently and there are also two LED acting as indicators.

Dual Power Supply Construction

This power supply circuit was built up on Veroboard as it is quite simple to build. Heatsinks can be mounted to the two regulators to improve the current drive capability. The transformer and circuit were mounted inside a wooden box. If a metal box is used the box must be connected to mains earth to prevent a shock hazard. Figure 2 shows a picture of the finished unit. It should be noted that this box is rather shabby and the author has been meaning to improve it for a while but it does do the job nicely.

Source: Tracking, Dual Rail Power Supply

This sensor circuit uses an ordinary NTC thermistor with a resistance of 47k at room temperature. A suitable part from Maplin Electronics is FX42V. The circuit is set in balance by adjusting the the 47k potentiometer. Any change in temperature will alter the balance of the circuit, the output of the op-amp will change and energize the relay. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.


At room temperature (25 degrees Celsius) a 47k NTC thermistor resistance is approximately 47k. The non-inverting op-amp input will then be roughly half the supply voltage, adjusting the 47k pot should allow the relay to close or remain open. To calibrate the device, the thermistor ideally needs to be at the required operating temperature. If this is for example, a hot water tank, then the resistance will decrease, one way to do this is use a multimeter on the resistance scale, read the thermistors resistance and then set the preset so that the circuit triggers at this temperature.

Please note that if the temperature then falls, the relay will de-energize. If the environment temperatures changes rapidly, then the relay may chatter, as there is no hysteresis in this circuit.

Hysteresis, allows a small amount of "backlash" to be tolerated. With a circuit employing hysteresis, there will be no relay chatter and the circuit will trigger at a defined temperature and require a different temperature to return to the normal state. Hysteresis can be applied to the circuit using feedback, try a 1 Mega resistor between op-amp output, pin 6 and the non-inverting input pin 2 to give the circuit hysteresis.

Without offset null adjustment, the output of the 741 IC will be around 2 Volts (quiescent) swinging to nearly full supply when triggered. The 4.7k and 1k resistor form a potential divder so that under quiescent conditions the transistor will be off. Quiescent or steady state means no signal, or in this case (when the temperature does not cause the output to swing to full voltage).

Source: Temperature Monitor

The meter movement itself will have a small resistance which will be part of the total 10K resistance, but it is usually low enough to ignore. The meter in the example below has a resistance of 86 ohms so the true resistor value needed would be 10K-86 or 9914 ohms. But using a 10K standard value will be within 1% so we can ignore the 86 ohms. For a full scale reading of 1 volt, the meter resistance would be more significant since it would be about 8% of the total 1K needed, so you would probably want to use a 914 ohm resistor, or 910 standard value.


By adding a parallel resistance, the milliamp meter can also be used to measure higher currents . The meter resistance now becomes very significant since to increase the range by a factor of ten, we need to bypass 9/10 of the total current with the parallel resistor. So, to convert the 1 milliamp meter to a 10 milliamp meter, we will need a parallel resistor of 86/9 = 9.56 ohms.

Source: Analog Milliamp Meter Used as Voltmeter

The main purpose of a metronome is to help the musician learn their music at the proper speed, usually so that they can then combine their part with other players in an ensemble

The digital metronome has following features:

• ATMEL AT92S1200(or higher) based: AVR 8 Bit RISC processor with timer.
• Range: 22.8 to 216 beats per minute w/ variable tuning-steps. Presets on 60, 120 and 180 bpm.
• Measure feature: an extra beat per 2/4, 3/4, 4/4 (the "measure").
• Precision: calibrated for 1MHz clocks and using timers (INTERUPT BASED). Other clocks possible.
• Load: approx. 20mA (due to driving the LED segments).

It is basically the processor with buttons and led and audio I/O, together with 4 LED segments. There are 3 segments for the BPM ("beats-per-minute") read-out and 1 for the 'measure' (2/4, 3/4, 4/4, disabled).

• SEGMENT #0: not used
• SEGMENT #1: the measure (output is 2 , 3 , 4 or 1 for 2/4, 3/4, 4/4 or NONE)
• SEGMENT #2-4: LED x1 (#2) , x10 (#3) and x100 (#4).

Metronome Schema and Source Code



Processor ATMEL AT92S1200 pin Layout The audio section produces a nice sound (which can be muted).

METRONOME: the assembler program for the AT92S1200 (or better) microprocessor.

Source: PROJECT: A Digital Metronome

CONCEPT OF OSCILLOMETRIC METHOD
This method is employed by the majority of automated non-invasive devices. A limb and its vasculature are compressed by an encircling, inflatable compression cuff. The blood pressure reading for systolic and diastolic blood pressure values are read at the parameter identification point.

The simplified measurement principle of the oscillometric method is a measurement of the amplitude of pressure change in the cuff as the cuff is inflated from above the systolic pressure. The amplitude suddenly grows larger as the pulse breaks through the occlusion. This is very close to systolic pressure. As the cuff ressure is further reduced, the pulsation increase in amplitude, reaches a maximum and then diminishes rapidly.

The index of diastolic pressure is taken where this rapid transition begins. Therefore, the systolic blood pressure (SBP) and diastolic blood pressure (DBP) are obtained by identifying the region where there is a rapid increase then decrease in the amplitude of the pulses respectively. Mean arterial pressure (MAP) is located at the point of maximum oscillation.


HARDWARE DESCRIPTION AND OPERATION
The cuff pressure is sensed by Freescale's integrated pressure X-ducer‰. The output of the sensor is split into two paths for two different purposes. One is used as the cuff pressure while the other is further processed by a circuit.

Since MPXV5050GP is signal-conditioned by its internal op-amp, the cuff pressure can be directly interfaced with an analog-to-digital (A/D) converter for digitization. The other path will filter and amplify the raw CP signal to extract an amplified version of the CP oscillations, which are caused by the expansion of the subject's arm each time pressure in the arm increases during cardiac systole.The output of the sensor consists of two signals; the oscillation signal ( ≈ 1 Hz) riding on the CP signal ( ≤ 0.04 Hz).

Hence, a 2-pole high pass filter is designed to block the CP signal before the amplification of the oscillation signal. If the CP signal is not properly attenuated, the baseline of the oscillation will not be constant and the amplitude of each oscillation will not have the same reference for comparison.

Oscillation signal amplifier together with the filter.


Digital Blood Pressure Meter Schematic



Author: C.S. Chua and Siew Mun Hin, Sensor Application Engineering Singapore, A/P
More about Digital Blood Pressure Meter

Even alkaline batteries become discharged relatively quickly because of the energy demands of the helicopter. Replacing the alkaline cells with six rechargeable NiMH batteries brought its own problems; the cell voltage is around 1.4 V after recharging but this quickly levels-out to 1.2 V once you begin drawing energy and this proved to be too low to recharge the helicopter battery. What is needed here is a voltage converter design small enough to fit into the space taken up by an AA battery which pumps up the voltage from the (now five rechargeable cells) up to the level produced by six alkaline batteries.

The author was not satisfied with the most simple design solution to the problem; it would be more useful if this booster cell could be used in any battery compartment irrespective of the number of cells. The number of batteries (n) would then be replaced by n–1 rechargeable cells (with one cell position taken up by the   booster) giving an output voltage the same as if n primary cells were fitted.

The circuit described here can be used in applications requiring four to ten primary cells. With the booster fitted, only three to nine rechargeable cells would be required. The use of (more bulky) electrolytic capacitors with a 35 V rating would allow the booster to be used in applications of up to 20 batteries.


In principle almost any switching regulator IC can be used in this way. The power output from this circuit with a LT1172 regulator is around 500 mA but it can be increased to 2 A for example by using the LT1170 instead.