BATTERY SWITCHING BOX
Ridiculously simple, this gadget has applications for the experimenter and service technician. Here are a few; you’ll think of others.
ELMER C. CARLSON
THIS SIMPLE AND INEXPENSIVE DEVICE HAS FOUND A number of uses. It has been particularly valuable in science fair projects and has also proven its worth in electronics testing and experimentation.
It uses only a few components: a DPDT. center-off switch, three pairs of 3-way binding posts, a battery holder, and an aluminum box. That, together with some solder and wire — and whatever batteries you choose to provide the voltage you need—makes up the entire parts list. The battery/switching box has paid for itself many times over.
Here are just several uses to which it can be put.
Even with the switch in the center-off position, the B \ T terminals are still connected to the battery. That allows connection of a voltmeter to monitor the battery voltage or voltage of a charger. If nickel-cadmium cells are used (Fig. 1) In fact, both the meter and charger may be used if one of them is connected to terminals or u. and the switch thrown to the appropriate position.
Two circuits may be powered from the same DC cells are used (Figure two) by connecting one of terminals A and the other to B. using the switch to select the circuit to which current will be supplied. Voltage can still be monitored at the BAT terminals.
The box can be used without batteries, too. Figure 3 shows an application where two sets of speakers, fed from the same audio source, can be compared at the flip of a switch. Of course comparisons of other things besides speakers can be made the same way.
Similarly, a single voltmeter as shown in Figure four can be used, by means of the switching box, to monitor voltages at two different test points without having to switch leads constantly. The box can also be used as a combination on/off switch and ammeter in / out selector (Figure 5).
The switching box can also be used to insert tw9 or three components (or component networks) into a circuit. It can alleviate the hazards of loose clip-leads and eliminate the frustrations of poor contacts and broken connections.
As is obvious from Fig. 6 there is nothing critical about parts or component placement. It would be advisable, though, to space the 3-way binding posts exactly 3/4 of an inch apart to accommodate the dual banana-plugs that are often found in laboratory environments.
There is very little to this project in the way of construction, but the applications that have been given here are only a few of the possibilities that will occur to you as you begin to use this simple but versatile device.
Copyright by Bill Bytheway, K7TTY February 2012