Thursday, May 29, 2014

Semi Conductor Tester - SemTest Part 4

Testing was done in part 3, this last part is consist of following:
Final assembly
The front panel assembly can now be lowered down onto the case. Make sure that the three ribbon cables are folded neatly into the space above the lower PCB and not caught between the edges of the case or lid. Fasten the case together with four M4 screws into the corner holes, then fit the knobs to the rotary switch and the pot and the assembly is complete. 

Testing the HV crowbar
It’s now necessary to check that the HV crowbar circuit is working correctly. To do this, power up the unit, wait a few seconds and then press the Menu Select button. You will get a display like this:
Device to Test:▲
Press Enter and then the Up button. The display will then show:
Test parameter:▲
Press Enter again. Set the Device Operating Voltage to 25V, using the right-hand knob. Then press the Test On/Off button to start the test.

Friday, January 11, 2013

Infrared audio headphone link for TV

To listen via headphones preferably good ‘surround your ears’ muff-type headphones, which not only deliver the wanted sounds directly to your ears and hearing aid(s) but also cut back the competing sounds at the same time. If you pick the right kind of headphones, with some acoustic damping in the earmuffs, they don’t cause your hearing aid(s) to emit feedback and whistle sounds either.

The result is comfortable listening at a volume level that’s right for you, where you can hear and understand everything that’s being said.

Headphone jack
Some TV sets do have earphone jacks, so you could simply fit a pair of stereo headphones with their own volume control (if necessary), plus a long cord and plug to mate with the jack on the TV. But many sets do not have a headphone jack, and many that do have it wired so that when headphones are plugged in, the speakers are disabled.

That’s fine for you, but no good for everyone else. In any case, being hooked up to the TV via a long cable has its own problems: you can forget to take ’em off when you get up for a comfort break or someone else can trip on the cable when they move about the room.

Friday, January 4, 2013

Ultrasonic Transmitter and Receiver

THE Ultrasonic Transmitter circuit shown in Fig. generates ultrasonic sound waves at a  frequency of 40kHz. The key component is a 555 timer, IC1, which is wired as an astable to produce an output frequency of 40kHz. This stream of electrical signals drives the ultrasonic
transmitter transducer TX1.

Potentiometer VR1, used as a variable resistor, enables you to make fine adjustment to the frequency when setting up the control system to ensure that TX1 is resonating at its optimum natural frequency, thereby ensuring maximum range. This adjustment is described in the ‘synchronising’ section at the end of the receiver section.

ultrasonic transmitter circuit

Friday, December 21, 2012

12V-24V High-Current Motor Speed Controller Part-3

In first part we discussed about the detail of circuit, back EMF and Mosfet protection; and in second part we covered the display and menu, in this third and last part we will build and test our project. 

The DC Motor Speed Controller is built on two PC boards: a main board, and a display  board. These are joined together via a 12-way flat ribbon cable, which plugs into a pin header on the main board. 

The main board can be assembled first – see Fig.9. Start by checking the PC board for hairline cracks and for any visible shorts across the copper tracks, especially between the ground plane and any adjacent tracks. In addition, check the hole sizes for the larger hardware items by test fitting these parts into position.

Making a link
That done, begin by installing the 17 wire links. These must go in first, since some of them run underneath some components.

To straighten the link wire, first clamp one end in a vice, then stretch it slightly by pulling on the other end with a pair of pliers. It’s then just a matter of cutting the links to length and bending their leads down through 90° to match the holes in the PC board.

Saturday, December 15, 2012

12-24v High Current Motor Speed Controller Part 2

In first part we discussed about the detail of circuit, back EMF and Mosfet protection; in the second part we will cover these:

Other protection measures
As already mentioned, diode D1 provides reverse polarity protection for microcontroller IC1 and the switchmode supply (IC2). Zener diode ZD1 is self-protecting in the case of reverse supply connection. However, if the supply is reversed, there will be a heavy conduction path via fast recovery diode D3 and the internal substrate diodes in the four power MOSFETs. If you are lucky, the 50A fuse will blow before the MOSFETs are damaged, but there is no  guarantee of this. SO dOn’T rEVErSE THE bATTErY cOnnEcTIOnS!

In a similar vein, if the outputs are shorted while power is applied, high current will flow  through the MOSFETs. Again, if you are lucky, the 50A fuse will blow before the MOSFETs go up in smoke. In reality, the 50A fuse is there to stop a fire! SO dOn’T SHOrT THE OUTPUTS TO THE MOTOr.

If the motor is under heavy load and becomes stalled, high currents will flow in its armature.  Depending on the motor’s rating, this may or may not blow the fuse. If the fuse  does not blow during stall conditions of the motor, the MOSFETs should survive, although they may get very hot.