filter Strange behavior from variable-gain amplifier

Posted on Feb 5, 2014

It takes a voltage between 0. 4 and 1. 2 V on pin 5 to control its gain. In the first two versions of the circuit, I used logic ICs and/or counters and an op amp with a resistor network for a DAC to provide the voltage, and all worked well. This last week, I decided to try my hand at doing the same with an Arduino doing the logic work, and instead of an op amp DAC, I`m filtering a PWM

filter Strange behavior from variable-gain amplifier

Click here to download the full size of the above Circuit.

signal and feeding it to a darlington-pair voltage follower. It took a while to get it right, but now it works. The odd part is, the voltage range that produces the correct gain variation is completely different: 1. 22 V to 2. 25 V. I`m happy that it works, but I`m very curious as to why that is.

Visit page

Leave Comment

characters left:

Related Circuits

Color sensor

Color sensor. Colour sensor is an interesting project for hobbyists. The cir- cuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow.

Dew sensor

Dew sensor. Dew (condensed moisture) ad- versely affects the normal per- formance of sensitive electronic devices. A low-cost circuit described here can be used to.

Audio Visual Ringer

Audio Visual Ringer. Many a times one needs an extra telephone ringer in an ad-joining room to know if there is an incoming call. For example, if the telephone is installed in.

Multipurpose Circuit for telephone

Multipurpose Circuit for telephone. This add-on device for telephones can be connected in parallel to the telephone instrument. The circuit provides audio-visual indication of on-hook,.

Off line Telephone tester

Off line Telephone tester. Here is a circuit of an off-line telephone tester which does not require any telephone line for testing a telephone instrument. The circuit is so simple that.

Telephone Headgear

Telephone Headgear. Acompact, inexpensive and low component count telecom head- set can be constructed using two readily available transistors and a few other electronic.

Telephone line based audio muting and light on circuit

Telephone line based audio muting and light on circuit. Very often when enjoying music or watching TV at high audio level, we may not be able to hear a telephone ring and thus miss an important...

Telephone Ringer using 556 dual timers

Telephone Ringer using 556 dual timers. Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone. The.

New Circuits

Zero consumption Anti-theft High power Code Switch for E-Bike Batteries

This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
Ultrasonic distance finder circuit

The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Simple Metal detector circuit with CD4030

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Fully automatic watering circuit for flower pots

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
Simple deep searching metal detector circuit

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
Sub-Harmonic Bass Converter for Electric Guitars

The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
Echo Depth Sounding Sonar for Boats

In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
100W HiFi Audio Amplifier Circuit

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
Plant-Pot Water Level Indicator Circuit

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....

Create NOW your QR MENU for your Restaurant / Hotel / Bar / Caffe,

Comprehensive ordering/paying features. fully personalized to suit your Business.

Update Anytime! Easy and Simple!

Popular Circuits

Altimeter Circuit

The circuit is powered by the receiver's pack, the current drain is low, specially if compared to...

STHS Computer Technology

On the breadboard, build two bi-directional motor control circuits (also known as "H-bridge")...

simple bus level-shift / I2C mosfet level converter Fairchild BSS138

While doing some background reading about the Philips I2C bus I came across an application note...

arduino temperature and light sensor

This device just sends data about the state of our office to Twitter (mainly because it`s just...

12v power supply circuit

Here is a very simple and useful project of a 12V power supply circuit using LM7812 IC. LM7812 is...

Odd-ball PI circuit identification request and headroom question

This schematic is modified from an old Bell & Howell projector amp for model 302 - PP 6v6`s with...

PID Temperature Control circuit schematic

Connect the components. Take note of the connections for the transistor. Connect the 22 ohm load...

Tilt Alarm Circuit

This is a circuit where an alarm will go off once the circuit is tilted. Once the circuit is...

Luminescent Generator

When spun rapidly between the fingers, a bipolar stepper motor will generate around 10VAC. If...

PPMC and stepping motor driver IC dedicated connection circuit

PPMC external UChl 5804 shows four-phase stepping motor drive IC is shown moving down. It uses...