February 2008

• Keep functional blocks of circuits as modules or separate areas in a big PCB, this helps in testing and troubleshooting.
• Power circuits, digital circuits and analog circuits should have separate supplies and ground when possible.
• Inputs and Outputs are the points of electric abuse, opto isolate, use zener barriers with overrated devices.
• When a microwave oven is turned on, a big spike is caused in the power line due to heavy inrush current on start up, Even pumps and motors cause such short time surges. This causes tripping of electrical protection circuits.
• When a tree branch falls on the high voltage overhead electrical lines, they spark violently and supply trips.
• Big or tall trucks go in small roads they may snap all low level cable or telephone wires on their way.
• Do you need to turn on many equipments all at once? do it one after an other sequentially or use a timer for delays. This is because at peak power demand time, turning on all can cause your fuse to blow or worse.
• When you design an equipment keep the controls minimum, too many options and too many knobs and dials are not good ergonomics. For your equipment to be user friendly use simple navigation and not menus nested 6 deep.
• Wire and crimping of wires for supporting the high currents and high voltages must be carefully chosen. The copper cross section area gives its ability to carry current, the quality, thickness and flexibility of the insulation gives its voltage capability. The Tightness of the crimped contact will ensure long term reliability. Mechanical Stress prevention for all wiring is very important and guarded termination for user-operator safety.
• BTA16600 and triacs of this series from ST have the metal TO220 tab electrically insulated from the device.
• MOC3041 and others, switch triacs at zero crossover which reduces EMI-RFI and spikes. It means when the sine wave is close to zero volts the triac is turned on.
• You have to ensure proper air circulation and fix proper heat-sinks with thermally conductive heat-sink compound or silicone grease with alumina. Anodized Aluminum heat-sinks with large surface areas and small fans are used in power electronic products for this purpose. If a component works very hot the specs will get derated, precision is lost and undesirable and unpredictable results will happen.

Here is is Digital Timer Learning Gadget. The buttons make a sound and Light up internal LED lamps. Power On-Off control, Digital Timer; Start, Reset Scroll and Select are the controls. This will simulate the operation of a microcontroller based digital timer.

Project Page programmable-digital-timer Rev-12 - Add to Webpage

Press The Power on-off for a soft start, this is to prevent the inrush current from stressing the javascript components. Then it goes to a display test. The Start button can run or stop timer by toggling. The reset will Bring timer to 0000, format is min-sec.

Set by pressing select to get a marker over orange digit, Use Scroll to set number. Press Start to start timer, Start to be off to set again. The buzzer will turn on when Time elapsed matches time set. and the alarm relay trips. And a Flashing Annunciator signals end of process. Now Reset will start process again and stop flashing LED.

To use this like a regular instrument, you need a small portable hand-held computer with browser. Fix that in a Cabinet by filing or grinding it to size and wire the relays and supply.