Hobby Projects - Insulation tester, LED Circuits, Meters.

Wednesday, September 16, 2015

Raspberry Pi - ARM with Linux Nano Computer

Raspberry Pi is a Miniature Computer that can Interface with a Display Device like TV and a keyboard.

Raspberry Pi a teeny weeny Computer

Model A has been redesigned to have 256Mb RAM, one USB port and no Ethernet (network connection). Model B has 256Mb RAM, 2 USB port and an Ethernet port.

The Raspberry Pi measures 85.60mm x 53.98mm x 17mm, with a little overlap for the SD card and connectors which project over the edges. It weighs 45g.

Raspberry Pi a teeny weeny Computer

The SoC is a Broadcom BCM2835. This contains an ARM1176JZFS, with floating point, running at 700Mhz, and a Videocore 4 GPU. The GPU is capable of BluRay quality playback, using H.264 at 40MBits/s. It has a fast 3D core accessed using the supplied OpenGL ES2.0 and OpenVG libraries.
Overall real world performance is something like a 300MHz Pentium 2, only with much, much swankier graphics.

There is composite and HDMI out on the board, so you can hook it up to an old analogue TV, to a digital TV or to a DVI monitor. No VGA support.

Wednesday, September 09, 2015

The Blobz Guide to Electric Circuits

Enter the Blobz Guide to Electric Circuits. - developed by Andy Thelwell at Staffordshire University. This is an excellent starter for youngsters to learn electricity.

The Blobz Guide to Electric Circuits

The Blobz Guide to Electric Circuits

This was a Tutor that started with the early-web means after Y2K times. This also used flash very creatively to make a web multimedia interactive tutor.

You can learn about battery, wire, switch and flow of electronics and the basic concepts that make electrical and electronic circuits. This is both useful for children and older people unfamiliar with electrons and their antics.

Saturday, September 05, 2015

Diode Thermometer

Measurement Of Temperature - When power transistors are used, they may tend to over heat. Likewise resistors may also overheat in the event of faults or short-circuits. The knowledge of their temperatures may be advantageous. In addition, measurement of temperature constitutes a basic necessity in day-to-day life.

Measuring the temperature of a body, depends upon the establishment of thermo-dynamic equilibrium between the body and the device used to sense the temperature. In practice, this condition is rarely attained since it is difficult to establish complete instantaneous equilibrium. Hence great care must be exercised in choosing a method suited to the problem so that satisfactory conditions for temperature measurements are obtained. Temperature sensors possess thermal characteristics dependent largely on their size and shape and the materials from which they are made.

These characteristics affect precise measurements. The introduction of a temperature sensor into a body tends to modify the temperature conditions at that point. In most cases the sensor is connected to a recording instrument by means of an intermediate system, along which the signal is carried. The intermediate system and the recorder may be subject to temperature and other changes. Hence compensating devices become a necessity to reduce or eliminate errors.

Diode Thermometer

The measurement of temperature in our instrument depends on the fact that the forward voltage drop of a silicon diode changes by about - 2 millivolts per degree centigrade. Thus, by measuring the change in forward voltage of silicon diode kept in a temperature probe, the voltage drop can be converted into temperature.

Since this involves the measurement of millivolt level accurately a precision voltage source is needed. This can be conveniently obtained from the 3 pin + 5v voltage regulator. This voltage is tapped using a preset VR6 whose output is used for adjusting the ice bath temperature reading to zero degree. This tapped voltage is fed to the diode in the temperature probe and the other end of the diode is returned to a negative supply of -8v. The negative supply uses a (-8v regulated output from IC 7808 voltage regulator) which has the least variation with temperature. Now, the voltage at the probe point is connected to the input of DPM via function selector switch ST.

The temperature probe can be made by a length of shielded audio cable connected to any type of mini plug and fitted onto the front panel socket SSG/T. The free end of the cable is soldered to the diode. The diode is kept just at the tip of the cable. A miniature glass diode like 1N4148 is preferred. The soldering makes a good fixture at the end of the cable. The meter can thus measure temperatures from 0°C to 150°C continuously and upto 200°C momentarily since above that the cable starts melting.

Epoxy Resin and a used Metal Pen Refill can be used to make a sensor to insulate the cable. The diode must be thermally and electrically isulated from metal tube.

(above text may have ocr and concept errors)

Extra Reading -