Tenma Resistance Decade Box

Probably useful for school/education use, but otherwise I don't think many people use such a device (primarily because most circuits don't

require a critical resistance, and if it does, then chances are that the value may need to be assembled with parallel resistors to create an

unusual value (and more than one of these resistance boxes would be very expensive). Furthermore most circuits operate at high frequencies,

so a decade box is difficult to insert into these circuits.

A variable resistor and an ohmmeter would be more useful in some situations, or a bag of mixed resistor values.

   I don't think you are correct on this assumption. These are used for bridge balancing, design, troubleshooting, and many other applications. These also come in capacitance and inductance models. Take a look at this company (I am not affiliated with this company in any way) and you might see what a large industry this is http://www.ietlabs.com/decaderes.html.

   I thought the same as you did when I came across one of these on eBay. I decided to look into exactly what these are used for and the amount of people who are in the market to purchase one. I was astounded when I saw the numbers and the high prices people will pay to buy one. I don't know why they don't just build one themselves as it is very simple, I guess people would rather just spend the money. I sell electronic components and Educational Electronic Kits so I am now looking into working on my own design for this product, maybe make some money off it. The basic model will run you around $100, I am sure I can build one much cheaper than that.

I would have to agree, even the recent Wireless Power Design Challenge, although I got a reasonable 9V DC supply from the system there still requires finer tuning. A decade box would be helpful but not needed in my application.

Although a reasonable experimental Decade box is really easy to build, I was able to make one with minimal fuss. It is also a good soldering technique build as well as I use 1/2W 0805 SMD Resistor with 1% tolerance in my build and also used thumbwheel switches that provide the easiest to read resistance value needed clearly seen.

I know if i needed critical voltage level in the 9V boost converter I would definitely need to use the decade for that.

Malcolm

WHAT!!!, the math provided in the data sheet is not enough, who would have thought

The math calculated the the resistance value but the voltage was 0.15V out. I did not worry too much about it as it was well within the tolerance of my project but to say that there maybe some applications that a decade box would be handy.

In electronics design for production tweaking by decade box is not a good technique - since it only sets up the one device you are tweaking. The usual practice is to calculate the spread of performance based on the tolerances of the components that will be used  - in this way it is possible to determine in advance if the design will work correctly when, some thousands or millions of parts later, the worst case combination of actual component values occurs.

Decade boxes are not often any use with high frequencies, (except nice expensive attenuators).

I've worked on my own as an electronic designer  for more than 12 years now and spent  a good deal of money on test gear, I've never bought a  decade box (R,C or L) and never missed one. They weren't often used previously even if they were around.

MK

I have to agree, but there are uses for them. I only made mine to help with replicating theoretical experiments. As a Radio Technician I never used anything like this but can only see application for some low power DC applications, most of all I wanted to play with low frequency OpAmp applications to look at stability. As a service technician doing my apprenticeship before OpAmps became common place the design requirements are very different to fixing a problem.

It is the reason I made mine as the purchase cost for something like this is a bit high for so little use. I still may simply stick in a resistor here and there without using a decade box.

Malcolm