The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.
In fact the max audio power x speaker (with 4 ohm impedance) using 12V is (Vsupply+ – Vsupply-)^2/(8*impedance) 12^2/32 = 4.5Watts per channel, that is laughable…
For powering correctly an amplifier the best is to use a symmetric supply with a high voltage differential. for example +20 – -20 = 40Volts
40^2/32 = 50 Watts per channel that is respectable.
This supply is intended for two channels with 50W max each (of course it depends on the amplifier used). Though it can be easily scaled up or the voltages changed to obtain different values.
Automotive 12V to +-20V converter (for audio amplifier) - [Link]
This is a simple servo tester which will comprehensively test the capabilities of almost any modern servo. It has two pushbuttons, CENTRE and SWEEP and a potentiometer which works as follows:
Simple Servo Tester - [Link]
This is an improved version of the Darkroom Timer originally created by Stan Ockers (1999). Some extra features were added and the PIC code was modified accordingly.
Darkroom Timer v2.0A for PCB Exposure Box - [Link]
This is a very simple, low cost, Hi-Fi quality power amplifier. You can build it 5 ways, like it’s shown in the table (from 20 W to 80 W RMS).
Motorola Hi-Fi power amplifier – [Link]
This is a spectacular but completely useless project. It lights Ultra-Bright LEDs in a sequence and each LED flashes brightly very briefly. The LEDs light-up going around and around since they are mounted in a circle (on a CD), then they pause before chasing again. The very brief flash of each LED (15ms) and the pauses (1 second) reduce the average current so the battery should last a long time.
6V Ultra-Bright LED Chaser – [Link]
U1a operates as a low-noise microphone preamp. Its gain is only about 3.9 because the high output impedance of the drain of the FET inside the electret microphone causes U1as effective input resistor to be about 12.2K. C2 has a fairly high value in order to pass very low frequency (about 20 to 30Hz) heartbeat sounds.
Electronic Stethoscope - [Link]
The 60 Watt linear amplifier is simple all solid state circuit using power mosfet IRF840. The IRF series of power transistors are available in various voltage and power ratings. A single IRF840 can handle maximum power output of 125 watts.
60W Linear amplifier – [Link]
As a keen cyclist I am always looking for ways to be seen at night. I wanted something that was a novelty and would catch the motorists eye. So looking around at my fellow cyclists rear lights, I came up with the idea of ‘NITE-RIDER’. NINE extra bright LED’s running from left to right and right to left continuously. It could be constructed with red LEDs for use on the rear of the bike or white LED’s for an extra eye catcher on the front of the bike.
Nite Rider Lights – [Link]
1) IC1D is a CMOS Schmitt trigger oscillator at about 2KHz. It starts and continues to oscillate with a supply down to 1.24V (the lowest output voltage of my LM317 variable power supply) or less.
2) IC1A is an inverter.
3) IC1B is a Schmitt trigger NAND gate. Its output is low only when both inputs are at, or higher than the upper Schmitt trigger threshold voltage.
Plants Watering Watcher - [Link]
This circuit controls a load (in this case a dc brushless fan) based on a temperature compared with a setpoint. THe transduced is a diode in the forward polarization regime. In fact when forward biased, the forward voltage drop accross a diode has a temperature dependance, in particular has a negative linear(ish) slope. This because of the boltzmann distribuition, causing electrons to pass to the conduction band thermically, lowering the voltage drop accross the diode.
On-Off Temperature Control – [Link]