Pink (Flicker) Noise Generator Circuit

This is a circuit for a flicker noise generator, an implementation of flicker noise analog modeling presented in NBS technical note #604, “Efficient Numerical and Analog Modeling of Flicker Noise Processes” by J.A. Barnes and Stephen Jarvis, Jr. With the component values shown the schematic diagram, the circuit will give a 1/f noise slope from below 1Hz  to over 4KHz. A TLC2272 op-amp is used for this circuit, but any low noise op-amps will work. This is the figure of the circuit;

The op-amp must be a low noise type because the noise generation comes from a high value resistor generating about 50nV noise. Use an op-amp with noise voltage less than 15 nV/root-Hz and noise current less than 0.1 pA/root-Hz, an easy-to-find feature in many low-noise modern op-amp devices. To simplify the construction, the capacitor values is slightly different from the calculated values described in the paper, and a bias circuit is provided to allow the use of polarized electrolytic capacitor. Because the electrolytic capacitor has poor tolerance, it should be chosen carefully for best performance. Compared to circuit utilizing diode zener, reverse-biased transistor, or other noisy devices, this circuit give more predictable and repeatable output level.  If we tap the output of the first op-amp through a 100uF capacitor (like as seen in the second op-amp), a precise 5uV/root-Hz white noise will be there as an excellent signal source for audio noise measurement calibration. At the second op-amp, this white noise is filtered to give a flicker noise (pink noise) frequency spectrum, since the pink noise is a subset of white noise in the frequency domain.

Passive Treble Control Circuit for Guitar Pedal

The R1/C1 network makes a low pass filter when the wiper is at the grounded end of the tone pot, and there is a treble cut. The C1 cap bypasses R2 when the wiper is adjusted so that it is at the top end of the pot and it creates a treble boost. This is the figure of the circuit;

The 100k output volume and the 100k tone pot are always in parallel as a constant load. It’s suggested to used a linear taper pot for the tone control and a log (audio) taper for the volume control. Suggested values for initial experimentation are R1=10k, R2=47k, and C1=0.022uF. Some signal loss, as with any passive network is the limitation of this combined tone control. However, many guitar pedal designs have strong enough output signal level, and this tone control is an excellent option for those circuits with enough drive.

Low Impedance Microphone Input Preamplifier Circuit

This is a circuit for a low-impedance (Z = 50 to 200 ohms) microphone input circuit or pre-amplifier that employs low-cost, low-noise precision operational amplifiers such as the OP27 and the OP37. This is the figure of the circuit;

The simple circuit above amplifies differential signals from low-impedance microphones by 50 dB.  Because of the high working gain of the circuit, use of the OP37 (which is a high-speed op amp) is recommended if bandwidth is important to the application.  To ensure stability, a dummy resistor Rp must be placed between the OP37 inputs. This will prevent amplifier oscillation due to 100% feedback from the open input in case the microphone is unplugged.     
 

IL300XC Isolation Amplifier Circuit for TMP01 Temperature Sensor

This is a design circuit for about IL300XC Isolation Amplifier circuit for TMP01 Temperature Sensor. This circuit is used in an environment that needs to be electrically isolated from the central processing area. This circuit uses an 8-pin opto isolator (IL300XC). IL300XC was chosen because it can operate across a 5,000V. To drive the LED connected between Pin 2 and Pin 1, this circuit uses an OP290 single-supply amplifier. The photodiode connected from Pin 3 to Pin 4 gives the feedback. This is the figure of the circuit;

The OP290 drives the LED, that there is enough current generated in the photodiode to exactly equal the current derived from the VPTAT voltage across the 470 kO resistor. On the receiving end, the current from the second photodiode is converted to a voltage through its feedback resistor R2. TO buffer the 2.5 V reference voltage of the TMP01, this circuit uses the other amplifier in the dual OP290. It will give the an accurate, low drift LED bias level without affecting the programmed hysteresis current. The bias level accuracy at receiving end is provided by A REF43.

The current of the photodiode is determined by following equation:
I1=(2.5V-VPTAT)/470K
The output voltage is determined by following equation:
Vout=2.5V-I2*R2
=2.5V-0.7*((2,5V-VPTAT)/470)*644K=VPTATT

R2 must be larger than R1 to achieve overall unity gain because the gain of IL300XC is less than 1.0. To correct for the initial gain accuracy of the IL300XC, A trim is used in this circuit. Just adjust the trim to get output voltage equal to VPTAT at any particular temperature. Both the OP90 and REF43 contribute no significant error because of drift and operate from a single supply.

Frequency Divider Circuit

This is a circuit for frequency divider circuit, or a circuit whose output frequency is a fraction of the frequency of its input.  The main component of this circuit is the 555, a versatile timer IC.  In this circuit, it is configured as a mono stable multi vibrator, i.e., it will output a single pulse at pin 3 every time its pin 2 is 'triggered' by a pulse. This is the figure of the circuit;

The width of the output pulse at pin 3 of the circuit above is defined by the product of R1 and C1, i.e., increasing the value of R1C1 will increase the output pulse width. Once the circuit above is triggered by a pulse at pin 2, the pin 3 output pulse cycle defined by R1C1 will first have to be completed before any subsequent pulses at pin 2 can trigger the circuit again. R1C1 of the circuit above can therefore be adjusted to define the number of input pulses equivalent to a single output pulse. Thus, this circuit is in effect dividing the input frequency by an integer.

Solar Charger Circuit

This is a design circuit for a solar charger circuit to charge Lead Acid or Ni-Cd batteries using solar energy. The circuit harvests solar energy to charge a 6 volt 4.5 Ah rechargeable battery for various applications. The charger has Voltage and Current regulation and Over voltage cut off facilities. This is the figure of the circuit;

The circuit uses a 12 volt solar panel and a variable voltage regulator IC LM 317. The solar panel consists of solar cells each rated at 1.2 volts. 12 volt DC is available from the panel to charge the battery. Charging current passes through D1 to the voltage regulator IC LM 317. By adjusting its Adjust pin, output voltage and current can be regulated. VR is placed between the adjust pin and ground to provide an output voltage of 9 volts to the battery. Resistor R3 Restrict the charging current and diode D2 prevents discharge of current from the battery. Transistor T1 and Zener diode ZD act as a cut off switch when the battery is full. Normally T1 is off and battery gets charging current. When the terminal voltage of the battery rises above 6.8 volts, Zener conducts and provides base current to T1. It then turns on grounding the output of LM 317 to stop charging. [Circuit schematic source: D. Mohankumar Notes].

Op Amp Digital to Analog Converter Circuit

This is a design circuit for a simple 4-bit digital-to-analog converter.  It is actually just a simple op amp summer circuit, i.e., an operational amplifier configured to output a voltage that is proportional to the sum of the input voltages. This is the figure of the circuit;

The op-amp summer circuit above works as a DAC because its input voltages are binary weighted with respect to each other, as set by the resistors (10K, 20K, 40K, 80K) at the inputs.  
 
The output Vo of this summer circuit w is:    
Vo = -VRef (5K) (S3/10K + S2/20K + S1/40K + S0/80K) = -VRef (S3/2 + S2/4 + S1/8 + S0/16) wherein S3, S2, S1, and S0 are the logic inputs ('1' or '0'). The number of bits of this DAC may be increased by connecting more switches with corresponding binary-weighted resistors to the inputs.

Wheatston Bridge PWM Signal Conditioner Circuit

This is a schematic diagram of a Wheatston Bridge PWM Signal Conditioner circuit. This circuit uses the MAX1452 signal conditioner. A ratiometric compensated output for the Wheatstone Bridge is generated by the MAX1452. Then the output of the Wheatston bridge is converted to a PWM output. the PWM-output duty cycle changes accordingly, as the MAX1452 output changes with pressure. the analog-output signal-conditioning ASICs can be used to substitute the MAX1452. This is the figure of the circuit;

 

Frequency counter with pulse-width-measurement option is the instrument that use the circuit. It need an accurate measurement of the PWM output’s pulse width. Beside that, a microcontroller can use the PWM output and the controller’s internal timer to calculate the time interval between high-to-low and low-to-high transitions.  To calculate coefficients required to program the signal-conditioning IC, the measured PWM value can be used. [Circuit schematic source: MAXIM-IC.com]

AD586/597 Temperature Transducer (Sensor) Circuit

This is a circuit for a stand alone temperature transducer/sensor circuit. This device uses The AD596/AD597, employing its internal junction compensation temperature sensor inside. This device can be used as temperature sensor by omitting the thermocouple and connecting the inputs (Pins 1 and 2) to common. This is the figure of the circuit;

The output will reflect the compensation voltage and the AD596/AD597 temperature will be indicated by the output. the AD596/AD597 will be operated over the full extended –55°C to +125°C temperature range. This device has output scaling of 10.1 mV per°C with the AD597 and 9.6 mV per °C with the AD596. when AD596 is used in temperature sensing mode, it will read slightly high, because there is 42mV offset.