Electrical Resistance Indicator for the Classroom









Unit 4F
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Technical Stuff
Technical Stuff

ERIC uses a LED to display current, rather than some kind of numerical display or a meter, to take advantage of the characteristics of the human eye. People's eyes can cope with a very wide dynamic range. They can detect changes in light level over several decades of light level using an approximately logarithmic response. Consequently ERIC can show changes in resistance over a similar dynamic range.

I tried using an ohmmeter instead of the light and I found that I was forever changing resistance range. This destroys the simple interactivity that ERIC offers.

You should note that the sensitivity of your eye depends on the ambient light. You will find ERIC less clear to use in direct sunlight. In particular, when you want to detect a current that has passed through many children, you will probably find it easier in a darkened room. ERIC is probably a Winter experiment rather than a Summer one.

ERIC uses an amplifier between the contacts and the LED. The maximum current that can pass between the contacts is 100 microamps. Whilst this would be visible passing through the LED, it is much better with the amplifier to give full brightness.

ERIC uses a 9 volt battery. DO NOT USE HIGHER VOLTAGES. Discourage children from experiments using multiple 9 volt batteries with a single ERIC.

ERIC takes small currents from the battery so it will last for a long time. It is worth replacing the battery every year or so to ensure that it doesn't leak. It is not recommended to use rechargeable batteries. Ensure that there is no connection between the contacts or disconnect the battery before storage.

If the battery is shorted, for example by putting a metal object across the battery contacts, it will get hot. Ensure that the battery contacts are not shorted during storage.

 You can email queries to us at:- sales@swallow.co.uk

First published 2/1/08

Date Last Modified: 2/1/08 Copyright @2008 Swallow Systems