555 Fish Feeding Timer Explanation

Overview

The project makes use of a monostable 555 timer circuit and a relay to drive the load in order to create an aquarium feeding timer.

Explanation

The setup of the circuit is a one shot trigger or timer where the 55 timer functions as the heart of the multivibrator. The relay is triggered by adding current capacity and all of the other components are for circuit protection. When triggered, the monostable circuit produces a single output pulse as it is stable in just one state. The device is silent and has reliable operation. It has an easily adjustable feeding window with low component count.

During operation, the return pump is connected to the Normally Closed side of the relay. The timers output is LOW and the relay is OFF during normal operation. The timing cycle starts and the relay output transistor conducts when the trigger button is pushed. This causes the return pump to de-energize by pulling the relay contacts to the Normally Open position. The output transistor stops conducting and the relay returns to the Normally Closed operating position when the timing period ends which allows restarting the return pump.

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Constructing an Antweight R/C Combat Robot

Overview

The project uses a Sabertooth 2X5 R/C in order to make a simple antweight R/C combat robot.

Explanation

The Sabertooth 2X5 R/C will be used to vary the motor speed to drive the robot around and to interpret signals from a radio control system. The Sabertooth will power the receiver using an internal 5V regulator. The receiver picks up the control info and will signal the information back to the Sabertooth. The Sabertooth will vary the voltage and direction going to the motors as it processes the information. The robot is able to drive at different speeds and turn left and right by varying the voltage going to the motors.

The 2 motors are wired in parallel with each other so they will appear as one motor to the Sabertooth. Constructing the chassis takes most of the time especially without the appropriate tools. Soldering is applied during the setup of the motors. An 800mAh lithium pack battery is used as the power source which keeps things really small and light. A hobby radio control transmitter and receiver are needed to remotely control the robot. Motor driver configuration is done to DIP switches.

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Time-Lapse Photography Known as CamTim

Overview

Any digital camera with a remote can be used for time-lapse photography of nature, continuous shooting of an event or for monitoring applications including research and security applications by creating this CamTim as a simple electronic circuit hack.

Explanation

The design of the CamTim makes it possible to be used in an external trigger mode where a wireless source or an external sensor operating on TTL voltages provides the trigger. For bird and wildlife photography, this comes very handy. To select the camera delay, the CamTim consists of a set of switches. The switch values are read by a microcontroller where a pulse train is also generated. To periodically close the remote switch of the camera, an interface circuit is created. The switches in the CamTim are set from 20uS to 40 minutes to select the camera trigger delay. To trigger a solenoid followed by triggering the remote control, the PIC16F84A microcontroller loops indefinitely.

The back EMFs are prevented from reaching the MCU by the diode as the solenoid is driven by an amplifier. The MCU is isolated from the solenoid using an optocoupler in order to produce good design.

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Explanation Electric Airplanes Engine Sound Synthesizer

Overview

The project utilizes the Tini2138 module in order to create an airplane sound generator system which illustrates the speed of the propeller being proportional to the pitch of the engine sound.

Explanation

The design includes a reflective optocoupler which comprises of a phototransistor and an infra-red LED. It is pointed towards the rotating body of the outrunner brushless electric motor. On the half of the motor’s perimeter is a white band and on the other half is a dark band. The sensor output is fed to an amplifier and a Schmitt trigger whose output is connected to one of the timer inputs of the microcontroller. The sampling period is set by the software in the microcontroller to a value proportional to the period measured by the sensor.

The various flight simulator models provide the engine sound files where the sounds are extracted. For the end of the loop to mesh seamlessly with the beginning, a program finds the appropriate breaking points, which is also used to automatically extract suitably short sound loops. The sensor board contains a quad op-amp chip and 4 potentiometers to select the sound and adjust the coefficient.

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Using Infra-Red Transmitter Cable TV Changer

Overview

The project is a PC controlled cable TV changer which uses an Infra-Red LED and a Microchip PIC microcontroller.

Explanation

During a recording, the device is designed to change channels on the cable TV set-top box. The correct waveform for the digits to be sent are created as a very simple program on the computer sends the channel number over RS232 to this PIC based IR transmitter. An unusual coding format is being used by the very old cable TV box which most programmable remote controls cannot be covered. But it is possible to decode them in order for the correct signals to be generated for the digits by capturing the signals.

A single transistor switch provides sufficient current and switches an LED as the function itself is very simple with just a PIC with a serial interface. The 5V power supply and 5V TTL levels are provided by a very nice FTDI USB to serial converter cable. The PCB has the serial connector, the transistor switch, and at the center is the PIC device. The incoming digits are converted to 17 bits of data by small amount of processing.

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