Sunday, 5 May 2013

The Audio Video Distribution Amplifier

With the amount of equipment in home entertainment centers today the need to be able to vary the gain of the audio or video signal is needed. I found this particular circuit helpful when used in conjunction with the Universal Descrambler and a Stabilizer circuit I built for making copies of video tapes. It not only allowed me the ability to fine tune the video strength it also helped me increase the recorded audio which typically becomes poor when making tape copies. Circuit operation is straight forward for amplifier circuits. The second channel for the audio amplifier is made up of the same components except the other half of IC1 is used. Pin 6 & 5 are inputs and 7 is the output.

Circuit Diagram
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Tuesday, 30 April 2013

Low Cost Step Down Converter With Wide Input Voltage Range

The circuit described here is mostly aimed at development engineers who are looking for an economical step-down converter which offers a wide input voltage range. As a rule this type of circuit employs a step-down converter with integrated switching element. However, by using a more discrete solution it is possible to reduce the total cost of the step-down converter, especially when manufacturing in quantity. The TL5001A is a low-cost PWM controller which is ideal for this project. The input voltage range for the step-down converter described here is from 8 V to 30 V, with an output voltage of 5 V and a maximum output current of 1.5 A.


When the input voltage is applied the PWM output of IC1 is enabled, taking one end of the voltage divider formed by R1 and R2 to ground potential. The current through the voltage divider will then be at most 25 mA: this value is obtained by dividing the maximum input voltage (30 V) minus the saturation voltage of the output driver (2 V) by the total resistance of the voltage divider (1.1 kΩ). T1 and T3 together form an NPN/PNP driver stage to charge the gate capacitance of P-channel MOSFET T2 as quickly as possible, and then, at the turn-off point, discharge it again.

The base-emitter junction of T3 goes into a conducting state when the PWM output is active and a voltage is dropped across R2. T3 will then also conduct from collector to emitter and the gate capacitance of T2 will be discharged down to about 800 mV. The P-channel MOSFET will then conduct from drain to source. If the open-collector output of the controller is deactivated, a negligibly small current flows through resistor R2 and the base of T1 will be raised to the input voltage level. The base-emitter junction of T1 will then conduct and the gate capacitance of T2 will be charged up to the input voltage level through the collector and emitter of T1.

The P-channel MOSFET will then no longer conduct from drain to source. This driver circuit constructed from discrete components is very fast, giving very quick switch-over times. Diodes D2 and D3 provide voltage limiting for the P-channel MOSFET, whose maximum gate-source voltage is 20 V. If the Zener voltage of diode D2 is exceeded it starts to conduct; when the forward voltage of diode D3 is also exceeded, the two diodes together clamp the gate-source voltage to approximately 19 V. The switching frequency is set at approximately 100 kHz, which gives a good compromise between efficiency and component size.

Finally, a few notes on component selection. All resistors are 1/16 W, 1 %. Apart from electrolytic C1 all the capacitors are ceramic types. For the two larger values (C2 and C5) the following are used:
  • C2 is a Murata type GRM21BR71C105KA01 ceramic capacitor, 1 µF, 16 V, X7R, 10 %;
  • C5 is a Murata type GRM32ER60J476ME20 ceramic capacitor, 47 µF, 6.3 V, X5R, 10 %. D1 (Fairchild type MBRS340T3) is a 40 V/3 A Schottky diode. Coil L1 is a Würth WE-PD power choke type 744771147, 47 µH, 2.21 A, 75 mΩ.
  • T1 (BC846) and T3 (BC856) are 60 V, 200 mA, 310 mW complementary bipolar transistors from Vishay. The TL5001AID (IC1) is a low-cost PWM controller with an open-collector output from Texas Instruments.

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Friday, 12 April 2013

USB Powered PIC Programmer

This simple circuit can be used to program the PIC16F84 and similar "flash memory" type parts. It uses a cheap 555 timer IC to generate the programming voltage from a +5V rail, allowing the circuit to be powered from a computer’s USB port. The 555 timer (IC1) is configured as a free-running oscillator, with a frequency of about 6.5kHz. The output of the timer drives four 100nF capacitors and 1N4148 diodes wir-ed in a Cockroft-Walton voltage multiplier configuration.

Circuit diagram:
usb-powered-pic-programmer-circuit-diagramw
USB-Powered PIC Programmer Circuit Diagram

The output of the multiplier is switched through to the MCLR/Vpp pin of the PIC during programming via a 4N28 optocoupler. Diodes ZD1 and D5 between the MCLR/Vpp pin and ground clamp the output of the multiplier to about 13.6V, ensuring that the maximum input voltage (Vihh) of the PIC is not exceeded. A 100kΩ resistor pulls the pin down to a valid logic low level (Vil) when the optocoupler is not conducting. The circuit is compatible with the popular "JDM" programmer, so can be used with supporting software such as "ICProg" (see http://www.ic-prog.com).
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Wednesday, 10 April 2013

IR Remote Control Receiver

With many audio systems consisting of separate units, you’ll often find that due to economic reasons only the amplifier has a remote control receiver module. The control signals are then sent to the other units using patch cables. The tuner and CD player, for example, won’t have a built-in receiver module. When the tuner from such a system is bought separately it can therefore not be used directly with a remote control, which is a big disadvantage in practice. The only way in which this can be accomplished is to connect an IR receiver to the input used by the patch cable. And that is exactly what this circuit is for. In practice it is not always clear which signal should be used and what its polarity should be.

IR Remote Control Receiver Circuit DiagramHowever, it will most likely be a demodulated signal. For these reasons we’ve combined a standard IR receiver module and two inverters. The first inverter also functions as a buffer, since the output of the module has a high impedance. The output of the receiver module is active low, so the first inverter outputs a non-inverting signal. The second inverter inverts this signal again. Jumper JP1 is used to select which of the signals is presented at the output. R2 protects the output from short circuits or possible over-loading of the electronics in the equipment it’s driving (for example when the input circuit uses 3 V logic).

R1/C1 suppress any possible supply spikes. Batteries are suitable for the power supply, because the circuit only takes about 1 mA. With a set of four rechargeable batteries with a capacity of 1800 mAh the circuit can function continuously for 2.5 months. Four NiMH cells and a charger are therefore perfect for the power supply. If you can be sure that the circuit will always be switched off when not in use, you could also use three ordinary alkaline batteries (AA cells). Because of their slightly larger capacity they will probably last for about half a year. When making your choice you should of course keep in mind that recharge-ables are better for the environment.
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Monday, 8 April 2013

Stereo Gain Audio Trim Control Circuit





Stereo Gain Audio Trim Control Circuit


This circuit using the MAX5160L digital pot in a divider chain
supplying the MAX4252 op amp with some positive feedback in addition to
the usual negative feedback via the 100K and 50K resistors. The gain
of this circuit can be shown to be:



AV = (1-Kn)/(Kp-Kn)



where Kn is the negative feedback fraction, Kp the positive feedback
fractions (for the example in Figure 4, Kn = 100K/(100K 50K) or 2/3,
and Kp is variable).



When the MAX5160L wiper is positioned at the VREF terminal, the gain of
the circuit is -0.5V/V, as there is no positive feedback contribution.
When the wiper is at mid scale, Kp = 0.5, and the gain is now -2V/V.
Hence, by using those 17 positions between VREF and midscale the gain
can be varied over a ±6dB range. The 15 unused positions have been
traded off for repeatability, as the gain value does not depend upon
the digital pot resistance tolerance, as did the circuit of Figure 1.
The gain tolerance is now only limited by the ±1% 100K/50K resistors,
and the INL/DNL error of the MAX5160L (±4.6% max.).



An interesting point to note, the limit for stability in this circuit
is reached when Kp ≥ 2/3, when the positive feedback fraction meets or
exceeds the negative. The host processor controlling the MAX5160L
should therefore prevent this situation occurring.



The circuit in Figure 5 shows an obvious appraoch to a 'traditional'
style volume control using digital pots. All codes are valid, with
settings ranging from 0dB to full attenuation. Table 1 shows the
calculated attenuations based on the MAX5160L's 32 steps.
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Saturday, 6 April 2013

Wiring Schematic and Schedule

From-To connector references are specified to form a point-to-point wiring list. Wiring schematics and schedules can then be generated automatically from the information included in the wire list and harness assembly drawing.
These schematic diagrams and schedules show the pin to pin wiring for all the connectors and wires in a harness design. The wiring details can be entered via HarnWare then the output can be drawn in Visio, the user has a choice to show the details as a Wiring Schematic or a Wiring Schedule (tabulated format).
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Thursday, 4 April 2013

Electronic Component Temperature Sensor

Electronic Component Temperature Sensor
Electronic Component Temperature Sensor
Electronic Component Temperature Sensor
Electronic components that are used for temperature sensors, among others: NTC, PTC, Thermostat, IC LM35 temperature sensor, temperature sensor IC LM335 etc. To create a series of simple electronics of the temperature sensor of the basic components of the temperature sensor, the component needs to connect to the transistors or Op-Amp as driving to the end of the circuit.

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