Softstarter

Switch-on surges are a major cause of appliance failure or blown fuses. Modern electronics such as plasma TVs or PC work stations can generate a huge ‘splat’ on the mains supply caused by their switched-mode power supplies or PSUs, which can blow some components, inflict wear on moving switch contacts or nuisance-trip the supply’s circuit breakers. See Please Take Note update.

 

Peak surges of several hundred amps can be caused when you turn some appliances on, so this Softstarter was designed to limit the inrush current and help overcome circuit breaker trips or component wear.  It uses a thermistor and extra switching circuit to reduce power waste.

 

Runs at mains voltage, intended for experienced constructors only.

 

6-Decade Resistance Substitution Box

For avid electronics hobbyists, this unit provides a million precision resistance values at the turn of a few rotary switches.

 

Unlike cheap resistance boxes that provide a few preferred values only, our design lets you dial in a precise value to enable you to experiment or refine a circuit on the bench. Offers any value from 10 ohms to 10M @ 1% tolerance. Single PCB carries all components for simple construction.

 

Semtest (Part 3)

This PICMicro-based design will test a wide range of active components, including LEDs, diodes, BJTs, MOSFETs, SCRs and more. You can even run tests on IGBTs and triacs. Menu-driven LCD display, multi-configuration ZIF connections connect to all common device pin-out styles. The circuit details are described in detail this month.

 

In Part 3 we describe the construction and setup procedure. Typical pinout diagrams are also included this month. An extra add-on crowbar kit is also suggested.

 

Jump Start (12)

Our series specially written for students and beginners offers an Egg Timer and explains the operation of the ubiquitous 555 timer i.c.   Circuit simulation and analysis using Circuit Wizard are encouraged and the article shows how a PCB can be created onscreen, step by step.

 

Also in this issue

 

• Max’s Cool Beans blog – Max muses over the evolution of the FPGA by Xilinx.
• PIC n MIX – our PIC-dedicated column builds on last month’s Real Time Clock
• Circuit Surgery – an intensive primer on op amp frequency response and gain-bandwidth product is offered by our in-house surgeon.
• Interface for PC users offers a variety of power supply circuits including the ICL7660 and MAX680
• Technotalk –  787 Dreamliner battery woes examined, and debunking the myth that LED lighting damages museum paintings
• Net Work – the Internet column – some incurable wireless network hassles, upgrading a PC for MIMO 802.11n wifi. PC cards described.

 

 

 

Files (PIC n MIX, graphics) 0413.zip

PCB files pcb0413.zip

 

Software for the Semtest project is in the February 2013 section of the Library.

 

Please Take Note

Soft Starter

In the June 2013 issue (p. 48) we advised that the PCBs available from the EPE PCB Service are single-sided and are only suitable for switching loads up to 10A.

 

If you require up to 20A (the maximum the relay is rated for) then two pieces of 22 swg (0.711mm) tinned copper wires must be soldered to the large PCB lands running from the relay contacts to the Live In and Live Out terminals, such ensuring the board can carry the load.