Friday 6 June 2014
Crystal Controlled Reflection Oscillator Circuit Diagram
How to build a Crystal-controlled-reflection-oscillator circuit diagram . This is a simple crystal controlled reflection oscillator circuit, this unit is easily tunable and stable, consumes little power, and costs less than other types of oscillators tlmt operate at the same frequencies. This unusual combination of features is made possible by a design concept that includes operation of the transistor well beyond the 3 dB frequency of its current-versus- frequency curve.
Crystal Controlled Reflection Oscillator Circuit Diagram
The concept takes advantage of newly available crystals that resonate at frequencies up to about 1 GHz.The emitter of transistor Q is connected with variable capacitor Cl and series-resonant crystal X. The emitter is also connected to ground through bias resistor Rl. The base is connected to the parallel combination of inductor L and capacitor C3 through DE-blocking capacitor and C4 and is forward biased with respect to the emitter by resistors R3 and R4.
Impedance Z could be the 220-0 resistor shown or any small impedance that enables the extraction of the output signal through coupling capacitor C2. If Z is a tuned circuit, it is tuned to the frequency of the crystal.
125MHz Dev Board with an ARM Cortex M3
The Simplecortex is a microcontroller development board that is shield compatible with the Arduino. The Simplecortex has a fast microcontroller, the LPC1769 from NXP. This is a ARM Cortex M3 microcontroller with 512KB flash, 64KB RAM and it runs at 120Mhz. To make sure that the Simplecortex is easy to use we made tutorials for almost every peripheral on the chip and examples to get you started.
There are tutorials for simple stuff like IO control up to more advanced tutorials for MicroSD cards. If you have ideas for a new tutorial or made a tutorial yourself, feel free to drop an email or post it in the forum. The Simplecortex also has an onboard debugger. It can also be used to program external devices like a self made PCB for your own project. No more microcontrollers with pre-programmed bootloader needed.
Wireless Sensor Applications using Dorji’f DRF5150S and DRf4432S Modules
Dorji Applied Technology from China builds different types of RF modules that can be easily incorporated in designing wireless data loggers, sensor network, telemetry and other wireless applications.
Some of their RF modules have an additional pre-programmed microcontroller that allows direct interface of selected analog and digital sensors to the module. This means you don’t need any external MCU or to write codes for these sensors. In this tutorial, Raj from Embedded Lab talks about their DRF5150S and DRF4432S RF modules which are very versatile and easy to use for wireless sensor applications. For illustrative purpose, Raj shows how to put them together to construct a simple wireless sensor application where data from a remote sensor are received and displayed on a PC, without using any external microcontrollers.
Digital Frequency Comparator Circuit Diagram
Here’s a digital frequency comparator for oscillators that indicates the result through a 7-segment display and a light-emitting diode (LED). When the frequency count of an oscillator is below ‘8,’ the corresponding LED remains turned off. As soon as the count reaches ‘8,’ the LED turns on and the 7-segment display shows ‘8.’
This demo circuit uses two NE555 timers configured as astable free-running oscillators, whose frequencies are to be compared.
The circuit of the digital frequency comparator portion comprises two 74LS90 decade counter ICs (IC2 and IC6), two 74LS47 7-segment display driver ICs (IC3 and IC7), 74LS74 set/reset flip-flop (IC4), 74LS00 NAND gate (IC8) and two 7-segment displays (DIS1 and DIS2). The astable free-running oscillators built around the timers are the frequency sources for the corresponding counters.
Digital Frequency Comparator Circuit Diagram
When power supply to the circuit is switched on, timing capacitor C1 starts charging through resistor R1 and potmeter VR1. When the capacitor voltage reaches 2/3Vcc, the internal comparator of IC1 triggers the flip-flop and the capacitor starts discharging towards ground though VR1. When the capacitor voltage reaches 1/3Vcc, the lower comparator of IC1 is triggered and the capacitor starts charging again. The charge-discharge cycle repeats. That means, the capacitor charges and discharges periodically between two-third and one-third of the power supply (Vcc). The output of NE555 is high during charging and low during discharging of capacitor C1.
The other oscillator (IC5) works similarly. The oscillator frequency can be varied by the potentiometer (VR1 or VR2). Output pins (pin 3) of the oscillators (IC1 and IC5) are connected to the respective decade counters (IC2 and IC6) through the DPDT switch.
IC2 and IC6 count the initial eight cycles. IC 74LS90 is a 4-bit ripple decade counter. It consists of a divide-by-two section and a divide-by-five section counter. Each section has a separate clock input. The input of the divide-by-five section (CP1) is externally connected to the P output (pin 12) of the divide-by-two section (CP0). When the divide-by-two section receives clock pulse, it becomes a divide-by-ten counter.
Decade counter 74LS90 is reset by a high pulse at its pins 2 and 3. Initially, pins 2 and 3 are pulled down by resistor R2. The P through S outputs of IC2 are connected to the A through D inputs of IC3. Pin 11 (S) of IC2 is also connected to pin 3 of IC4(A) for providing the clock pulse. The count is displayed on the 7-segment display.
The 7-segment decoder/driver (74LS47) accepts four binary-coded decimals (8421), generates their complements internally and decodes the data with seven AND/OR gates having the open-collector output to drive the display segments directly. Each segment-driver output is capable of sinking 40mA current in the ‘on’ state. Pins 3, 4 and 5 of the display driver are connected to Vcc to disable the ripple-blanking input (RBI), blanking input (BI)/ripple-blanking output (RBO) and lamp test (LT).
IC3 provides segment data to the 7-segment display through current-limiting resistors R3 through R9 (each 220 ohms).
IC 74LS74 (IC4) controls the reset pin (RST) of NE555. It is a dual D-type flip-flop with direct clear and set inputs and complementary outputs. The input data is transferred to the outputs on the positive edge of the clock pulse. Since the Q output is connected to the data input D, the flip-flops work in toggle mode.
Initially, reset pins 1 and 13 of the flip-flops are pulled high via resistor R10. When the reset pin of any flip-flop receives a low pulse from NAND gate N2 of IC8, the flip-flop is reset and its Q output goes high. On receiving a clock pulse, the Q and Q outputs of the flip-flop go high and low, respectively, and the LED turns on. The low output of IC4 resets the oscillators. The reset signal is derived with the help of NAND gates N3 and N4.
When switch S2 is pressed, both the oscillators and the respective counters start working. As soon as any of the counters counts ‘8,’ the corresponding display shows ‘8’ and LED glows. This means that oscillator has a higher frequency. Now both the counters stop counting because the flip-flop output goes low to reset both the astable oscillators.
In case the frequencies of both the stable oscillators are same, both the displays show ‘8’ and LED1 and LED2 glow at the same time.
Sourced By EFY Author V. Gopalakrishnan
Wideband Wien Oscillator Circuit with Single Gang Pot
This Wien bridge oscillator (after Max Wien, 1866–1938) produces a low-distortion sine wave of constant amplitude, from about 15 Hz to 150 kHz. It requires just four opamps and will work off a single 9-volt battery. Also, unlike most Wien bridge oscillators, it does not require a dual-gang potentiometer for tuning. Op amp IC2b provides an artificial ground so that the circuit will operate from a unipolar supply (9 V battery or power pack). IC2a is the main amplifier for the oscillator. The frequency range is divided into four decades by 2-pole, 4-way rotary switch SW1.
Wideband Wien Oscillator Circuit with Single-Gang Pot Circuit Diagram
Only one arm of the Wien network is varied, but the change in positive feedback that would normally result is compensated for by IC1b, which works to bootstrap R2, thereby changing the negative feedback enough to maintain oscillation. A linear change in the resistance of the tuning pot results in a roughly logarithmic change in frequency. To get a more conventional linear change a log-taper pot is used wired so that rotating the knob anticlockwise causes frequency to increase.
You could use an anti-log pot the other way around if you prefer, but these things are notoriously hard to find. IC1A is an integrator that monitors the amplitude of the output signal and drives an LED (D2). This must be mounted facing the LDR (light dependent resistor) and shielded from ambient light (for example, with a piece of heat-shrink tubing). IC1a is then able to control the gain of IC2a so that oscillation is maintained with minimum distortion.
The maximum output amplitude of the generator is about 2 Vp-p when the LED and LDR are mounted as close as possible. Distortion is less than 0.5 % in the lowest range, and too low for the author to measure in the higher ranges. Any LDR should work, provided its dark resistance is greater than 100 kO. If you do not have an LDR with such high resistance, try increasing R5 until oscillation starts. Breadboarded prototypes of the circuit were built by the author using dual and quad opamp packages, and both work equally well.
Wideband Wien Oscillator Circuit with Single-Gang Pot Circuit Diagram
Only one arm of the Wien network is varied, but the change in positive feedback that would normally result is compensated for by IC1b, which works to bootstrap R2, thereby changing the negative feedback enough to maintain oscillation. A linear change in the resistance of the tuning pot results in a roughly logarithmic change in frequency. To get a more conventional linear change a log-taper pot is used wired so that rotating the knob anticlockwise causes frequency to increase.
You could use an anti-log pot the other way around if you prefer, but these things are notoriously hard to find. IC1A is an integrator that monitors the amplitude of the output signal and drives an LED (D2). This must be mounted facing the LDR (light dependent resistor) and shielded from ambient light (for example, with a piece of heat-shrink tubing). IC1a is then able to control the gain of IC2a so that oscillation is maintained with minimum distortion.
The maximum output amplitude of the generator is about 2 Vp-p when the LED and LDR are mounted as close as possible. Distortion is less than 0.5 % in the lowest range, and too low for the author to measure in the higher ranges. Any LDR should work, provided its dark resistance is greater than 100 kO. If you do not have an LDR with such high resistance, try increasing R5 until oscillation starts. Breadboarded prototypes of the circuit were built by the author using dual and quad opamp packages, and both work equally well.
Author: Merlin Blencowe (Elektor)
Resistors:
R1,R2,R3,R6,R10,R11 = 10kO
R7 = 100kO
R4,R9,R12 = 100O
R5 = 12kO
R8 = 1kO
P1,P2 = 10kO potentiometer, logarithmic law
R13 = LDR, R(dark) >100kO, e.g. Excelitas Tech type
VT90N1 (Newark/Farnell # 2568243)
Capacitors:
C1,C5 = 1µF solid
C2,C6 = 100nF
C3,C7 = 10nF
C4,C8 = 1nF
C9-C12 = 47µF 16V, electrolytic, radial
Semiconductors:
D1,D2,D3 = 1N4148
D4 = LED, red, 5mm
IC1,IC2 = TL072ACP
Miscellaneous:
SW1 = 2-pole 4-position rotary switch, C&K Compo-
nents type RTAP42S04WFLSS
K1,K2 = PCB terminal block, 5mm pitch
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