Friday, January 10, 2014
Solar Charger Circuit Project Using Transistors
A very simple solar charger circuit project can be designed using few external electronic parts . This simple solar charger circuit is capable of handling charge currents of up to 1A. Alternate component values are given in the figure for lower current applications.
Solar Charger Circuit Project Using Transistors circuit diagram :
The only adjustment is the voltage trip point when the current is shunted through the transistor and load resistor. This should be set with a fully charged battery. As the transistor and R3 have the entire panel’s output across them when the battery is fully charged, all of the current from the panel will be going through R3 and the Darlington transistor TIP112, so these must be well heat sunk. Adjust R1 for the trip point, usually 14.4 V – 15 V for a 12 V SLA or a 12 V Ni-Cd battery.
Source : http://www.ecircuitslab.com/2011/06/solar-charger-circuit-project-using.html
Electric Guitar Violin Preamplifier
Magnetic pick-ups in musical instruments have a relatively high output impedance. This can result in a reduction in treble response when connected via a long cable run or to equipment with a low input impedance. This preamplifier provides a high input impedance and a low impedance output, solving both issues. It has adjustable voltage gain and can run off a battery or DC plugpack. The input signal is AC-coupled to the non-inverting input of IC1a, part of a TL074 quad op amp.
This has JFET input transistors and the input impedance is set by a 330kΩ bias resistor which also sets the DC level at this input to half supply (Vcc/2). This is generated by a voltage divider comprising two 10kΩ resistors and bypassed by a 47µF capacitor to reject noise and hum.
IC1a is configured as a non-inverting amplifier with a gain of between 2 and 20, depending on the setting of VR1. IC1a’s output is fed to VR2 via a 22µF capacitor, allowing the output volume to be set. The audio then passes to the non-inverting inputs of the remaining three op amps (IC1b-IC1d) which are connected in parallel to provide a low output impedance; it will drive a load impedance as low as 600Ω. The 100Ω resistors in series with the outputs provide short-circuit protection for the op amps and also prevent large currents from flowing between the outputs in case they have slightly different offset voltages.
The buffered signal is then AC-coupled to two output connectors using 47µF electrolytic capacitors. For Output 1, a 47kΩ resistor sets the output DC level to ground and a 220Ω series resistor provides further short-circuit protection. Output 2 is similar but includes another potentiometer (VR3) to allow its level to be set individually. Note that this means the impedance of Output 2 can be high (up to 2.5kΩ depending on the position of VR3’s wiper).
The total harmonic distortion of this circuit is typically less than 0.01% with the gain set to six. If a TL064 is used instead of a TL074, the current drain will decrease but there will be more noise at the output. Finally, the input impedance can be increased by increasing the value of the 330kΩ resistor to suit high-impedance pick-ups.
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This has JFET input transistors and the input impedance is set by a 330kΩ bias resistor which also sets the DC level at this input to half supply (Vcc/2). This is generated by a voltage divider comprising two 10kΩ resistors and bypassed by a 47µF capacitor to reject noise and hum.
IC1a is configured as a non-inverting amplifier with a gain of between 2 and 20, depending on the setting of VR1. IC1a’s output is fed to VR2 via a 22µF capacitor, allowing the output volume to be set. The audio then passes to the non-inverting inputs of the remaining three op amps (IC1b-IC1d) which are connected in parallel to provide a low output impedance; it will drive a load impedance as low as 600Ω. The 100Ω resistors in series with the outputs provide short-circuit protection for the op amps and also prevent large currents from flowing between the outputs in case they have slightly different offset voltages.
The buffered signal is then AC-coupled to two output connectors using 47µF electrolytic capacitors. For Output 1, a 47kΩ resistor sets the output DC level to ground and a 220Ω series resistor provides further short-circuit protection. Output 2 is similar but includes another potentiometer (VR3) to allow its level to be set individually. Note that this means the impedance of Output 2 can be high (up to 2.5kΩ depending on the position of VR3’s wiper).
The total harmonic distortion of this circuit is typically less than 0.01% with the gain set to six. If a TL064 is used instead of a TL074, the current drain will decrease but there will be more noise at the output. Finally, the input impedance can be increased by increasing the value of the 330kΩ resistor to suit high-impedance pick-ups.
Thursday, January 9, 2014
Electronic Code Lock
Nowadays, electronic code locks are usually based on microcontrollers. However, if you like your electronics discrete, you will enjoy the battery-operated circuit shown here. Since the circuit automatically switches off after the door has been opened and draws no current in the idle state, three alkaline batteries (mignon, AA or R6 cells) are good for around 5,000 door openings. The main advantage is that the door opener can also be powered from the battery, so it’s not necessary to run any extra cables.
Project Image :
Electronic Code Lock Schematic Circuit Image
Figure 1 shows the schematic diagram of the circuit, which is split into two parts. The first part is the control panel, which consists of a 12-position keypad and two LEDs. The second part is the programming and evaluation logic, which contains only standard logic ICs. The control panel is connected to the logic board by a 16-way flat cable. The keypad circuit is laid out with separate connections to the individual switches, instead of a matrix. The code is programmed using the two pin connector strips K1 and K2. The circuit allows any desired combination of numbers to be used for the code, up to a maximum of 9 positions. Press-ing a particular button, which in principle is random but which naturally must be specified in advance, awakens the circuit from the zero-current idle state. This Start button cannot be used in the subsequent code sequence. The Start button is programmed by connecting a wire bridge from the associated pin of K2 to pin 1 of K1. The code sequence is programmed in a similar manner. The first numeral of the code is programmed by connect-ing the associated pin of K2 to pin 2 of K1, the connection for the second numeral is made to pin 3 of K1, the third to pin 4 and so on. Numerals that are not used in the code do not actually have to be connected. However, if the unused buttons are connected to VDD, the code lock will assume that an error has occurred if any of these buttons is pressed and will reset the circuit. Pressing the Start button switches on transistor T1, which connects the supply voltage source to the code lock. This is indicated by the yellow LED (D20).
Circuit diagram :
Electronic Code Lock Schematic Circuit Diagram
Part List :
Resistors :
R1,R2 = not fittedR3 = 220kΩ
R4,R5 = 1MΩ
R6 = 220kΩ
R7,R9,R10,R17 = 100kΩ
R8,R12,R14 = 2MΩ2
R11 = 560Ω
R13,R15,R20 = 1kΩ5
R16 = 100kΩ
R18 = 120Ω
R19 = 10k
R21-R24 = 3Ω3
R25-R35 = 22kΩ
Capacitors :
C1,C6,C7,C8,C10 = 100nF
C2,C3,C5 = 10nF
C4 = 1µF
C9 = 330nF
C11 = 47µF 16V radial
Semiconductors :
D1-D9,D11,D13,D14,D15,D17,
D18 = 1N4148
D10,D12 = zener diode 1V2
0.4W*
D16 = 1N4001
D19 = LED, green
D20 = LED, yellow
T1 = BC327
T2,T3,T4 = BC337
T5 = BD140
IC1 = 4017
IC2,IC3 = 4069 or 40106
Miscellaneous :
JP1 = jumper
K1,K2 = 12-way pinheader or
wire links
K3,K4 = not required (ribbon
cable )
K5, K6 = 2-way PCB terminal
block, lead pitch 5mm
S1-S12 = pushbutton with
make contact
Since the logic ICs are now enabled, the output of IC3f will be High, so T2 also conducts and pulls the base of T1 to ground. This means that the Start button can be released without affecting the circuit. However, C11 can now slowly charge via the high resistance of R12 until the voltage at the inverter input is high enough to cause its output to go Low, which interrupts the supply voltage to the circuit and puts it back into the idle state. The valid code must therefore be entered during the time interval determined by this R–C time constant. Once the supply voltage is disconnected, C11 discharges rapidly via D18. This is important, since other-wise C11 could retain its charge for a long time. This would make the time allowed for entering the code significantly shorter the next time the lock is used. Pressing the Start button also has other consequences. Via the Start switch, ground potential arrives at IC2d, where it causes a pulse to be generated that places counter IC1 in a defined state (Q0 = 1) prior to the entry of the first code numeral. The first code numeral can now be entered. If the correct button is pressed, the High potential from Q0 passes through the closed switch to reach IC2d–IC2a. This net-work generates a positive pulse at the instant that the but-ton is released. This pulse clocks the counter, so that the High level from Q0 moves by one position to Q1. This process repeats itself until all code numerals have been entered.
PCB Layout :
Electronic Code Lock Schematic PCB Layout
After the ninth numeral has been entered, the positive volt-age jumps to Q9, where it charges C4 (if jumper JP1 is installed). While C4 is charging, the output of IC2e goes Low for approximately two seconds, and the output of IC3d goes high for the same interval. Power transistor T5 is switched on via R19 and T4 to supply current to the door opener. At the same time, IC3a switches on the green LED (D19) to indicate that the door can be opened. T3 limits the current through the door opener to around 700 mA. Once C4 is sufficiently charged, the output of IC2e changes to High. Not only does this switch off the door opener, but the positive edge also generates a pulse in the network IC2f/IC3c that passes through D14 to reach IC1 as a reset pulse (D14, D17 D13 and R7 together form a ‘wired-or’ gate). Inverter IC3b also provides the power-up reset to the counter. The reset signal places the circuit back into its initial state. What happens if an incorrect button is pushed? In such a case a Low level is passed through in place of the High level from the counter output. This has the same consequence as the Low level from the Start button: the counter is reset.
Note that you can also modify the circuit to use fewer than nine numerals for the code. All that is necessary is to connect C4 via a jumper to another counter output in place of Q9 (for example, to Q4 for a four-position code). The diode at the selected output of the counter can be replaced by a wire jumper, and the ‘higher level’ diodes can also be omit-ted. The active ‘on’ time of the door opener is 2 s. If this seems to be too short, the value of R8 or C4 can be increased. However, this also increases the amount of power drawn from the battery, especially considering that the door opener is by far the biggest power glutton in the circuit. In order to integrate the circuit into an existing door opener or to use it to operate an ac door opener, you should connect a relay to K5. Before assembling the circuit using the printed circuit board shown in Figure 2, you should separate the two sections by sawing between K3 and K4. The logic board should not be fitted directly behind the pushbuttons for entering the code. Instead, it is better to separate the entry pushbuttons, the LEDs and the door opener from the logic circuit board with a length of cable. Otherwise, a screw driver or a bit of wire connected between the emitter and collector of T5 is all that is needed to outfox the code lock and open the door.
Fitting the components to the circuit board should not be difficult. The ICs can be mounted in sockets. The author used 4049 inverter ICs, but in the Elektor Electronics lab prototype we used 4069’s, which are functionally compatible but not pin-compatible, and we also tried a 40106, which has Schmitt-trigger inputs. With a 4069, normal 1N4148 diodes can be used for D10 and D12. The best solution is to use the relatively noise-immune 40106. However, it is then necessary to use Zener diodes for D10 and D12, due to the higher threshold voltage. A 3.3-V type is ideal with an operating voltage of 15 V. There is one thing you should not overlook: with low-voltage zener diodes, the band on the package marks the anode instead of the cathode, as you would normally expect. At least, this is true in most cases, but not always.
Author : R. Heimann - Copyright : Elektor Electronics
12 V Glow Plug Converter
Most small internal-combustion engines commonly used in the model-building world use glow plugs for starting. Unfortunately, glow plugs have an operating voltage of 1.5 V, while fuel pumps, starter motors, chargers and the like generally run on 12 V. This means that a separate battery is always needed to power the glow plug. The standard solution is to use an additional 2-V lead storage battery, with a power diode in series to reduce the voltage by approximately 0.5 V. However, this has the annoying consequence that more than 30 percent of the energy is dissipated in the diode. Naturally, this is far from being efficient.
12-V Glow Plug Converter Circuit diagram :
The converter presented here allows glow plugs to be powered from the 12-V storage battery that is usually used for fuelling, charging, starting and so on. A car battery can also be used as a power source. Furthermore, this circuit is con-siderably more efficient than the approach of using a 2-V battery with a series power diode.
The heart of the DC/DC converter is IC1, a MAX 1627. The converter works according to the well-known step-down principle, using a coil and an electrolytic capacitor. Here the switching stage is not integrated into the IC, so we are free to select a FET according to the desired current level. In this case, we have selected a 2SJ349 (T1), but any other type of logic-level FET with a low value of RDSonwould also be satisfactory. Of course, the FET must be able to handle the required high currents.
Diode D1 is a fast Schottky diode, which must be rated to handle the charging currents for C2 and C3. This diode must also be a fairly hefty type. The internal resistances of coil L1 and capacitors C2 and C3 must be as low as possible. This ensures efficient conversion and prevents the components from becoming too warm.
The resistor network R2/R3 causes 87 percent of the output voltage to be applied to the FB pin of IC1. This means that an output voltage of 1.5 V will cause a voltage of approximately 1.3 V to be present at the FB pin. The IC always tries to drive the switching stage such that it ‘sees’ a voltage of 1.3 V on the FB input. If desired, a different output voltage can be provided by modifying the values of R2 and R3.
When assembling the circuit, ensure that C5 and C1 are placed as close as possible to IC1, and use sufficiently heavy wiring between the 12-V input and the 1-5-V output, since large cur-rents flow in this part of the circuit. A glow plug can easily draw around 5 A, and the charging current flowing through the coil and into C2 and C3 is a lot higher than this!
Source : http://www.ecircuitslab.com/2012/07/12-v-glow-plug-converter.html
Friday, December 27, 2013
Burglar Alarm With Timed Shutoff Circuit Diagram
When SI (sensor) is closed, power is applied to U2, a dual timer. After a time determined by C2, CI is energized after a predetermined time determined by the value of C5, pin 9 of U2 becomes low, switching off the transistor in the optoisolater, cutting anode current of SCR1 and de-energizing Kl. The system is now reset. Notice that (i6x C2) is less than (R7xC$). The ON time is approximately given by:(R7xC5)-(R6xC2) = Ton
Burglar Alarm With Timed Shutoff Circuit Diagram
Wednesday, December 25, 2013
Memory Save on Power down Circuit Diagram
Memory Save on Power down Circuit Diagram. The auxiliary output powers the memory, while the main output powers the system and is connected to the memory store pin. When power goes down, the main output goes low, commanding the memory to store. The auxiliary output then drops out.
Memory Save on Power down Circuit Diagram
/Monday, December 23, 2013
Build a 5 Zone alarm Circuit Diagram
This is a complete alarm system with 5 independent zonessuitable for a small office or home environment. It uses just 3CM IC`s and features a timed entry / exit zone, 4 immediatezones and a panic button. There are indicators for each zone a“system armed” indicator. The schematic is as follows:
5 Zone alarm Circuit Diagram
Circuit Notes:
Each zone uses a normally closed contact. These can be microswitches or standard alarm contacts (usually reed switches).Suitable switches can be bought from alarm shops and concealed indoor frames, or window ledges.Zone 1 is a timed zone which must be used as the entry andexit point of the building. Zones 2 – 5 are immediate zones,which will trigger the alarm with no delay. Some RF immunity isprovided for long wiring runs by the input capacitors, C1-C5. C7and R14 also form a transient suppresser. The key switch acts asthe Set/Unset and Reset switch. For good security thisshould be the metal type with a key.
Operation:
At switch on, C6 will charge via R11, this acts as the exitdelay and is set to around 30 seconds. This can be altered byvarying either C6 or R11. Once the timing period has elapsed,LED6 will light, meaning the system is armed. LED6 may be mountedexternally (at the bell box for example) and providesvisual indication that the system has set. Once set any contactthat opens will trigger the alarm, including Zone 1. To preventtriggering the alarm on entry to the building, the concealedre-entry switch must be operated. This will discharge C6 andstart the entry timer. The re-entry switch could be a concealedreed switch, located anywhere in a door frame, but invisibleto the eye. The panic switch, when pressed, will trigger thealarm when set. Relay contacts RLA1 provide the latch, RLA2operate the siren or buzzer.
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