Low Cost Programmable Decade Resistor for Prototyping Convenience

[Flump]

Thanks Gerry, PM sent

[zapta]

Mark,

The offer is still there, if you want to buy a stamp and an envelope and post me a pre-stamped empty envelope I will stick a few in the post for you - will save you a few quid

Gerry

Hi Gerry,

Have you consider offering optional casing for your resistor boards?  Even something as simple as an acrylic plate at the bottom with four screws.

[0xdeadbeef]

Don't want to undermine nice Gerry's project but for those who are looking for an affordable decade resistor with case and switches, this might be an option:
http://www.elv.de/praezisions-widerstandsdekade-wd-100-komplettbausatz.html

It's a pretty nice diy kit. Unfortunately, they increased the price since I bought two of them.
As far as I recall, they cost 20€ back then, but yeah well.

[gerrysweeney]

Mark,

The offer is still there, if you want to buy a stamp and an envelope and post me a pre-stamped empty envelope I will stick a few in the post for you - will save you a few quid

Gerry

Hi Gerry,

Have you consider offering optional casing for your resistor boards?  Even something as simple as an acrylic plate at the bottom with four screws.

Hi,

I did but the cost was prohibitive given I was designing to a budget.  Someone designed a snap-on case which can be bought here (and other places too I believe) http://www.sculpteo.com/en/print/resistor_decade_box/gpgZ4VM9?uuid=fRAyWJ0swpGAMTRdhAaGVd

Gerry

[gerrysweeney]

Thanks Gerry, PM sent

Hi Mark,

I did not have 2010's but have some slightly bigger that will fit the land pattern no problem, I have put a bunch of them in the post for you. Thanks for the stamped envelope.

Gerry

[Flump]

The resistors arrived today
thanks very much 

However the repair didn't go according to plan
so I shall order another from you soon

[gerrysweeney]

The resistors arrived today
thanks very much 

However the repair didn't go according to plan
so I shall order another from you soon

Why what happened?

[Flump]

I could not get the contacts on the larger resistors to contact the pads on the board
as they were longer than the originals, after carefully placing the resistor centrally over the pads
the resistor contact area was outside the solder pads so I tried to bridge them with solder and the
pads on the board lifted off.

It was my first time working with SMD's and I'm sticking to that exscuse 

[zapta]

Hi,

I did but the cost was prohibitive given I was designing to a budget.  Someone designed a snap-on case which can be bought here (and other places too I believe) http://www.sculpteo.com/en/print/resistor_decade_box/gpgZ4VM9?uuid=fRAyWJ0swpGAMTRdhAaGVd

Gerry

Thanks. Yesterday I took a class of 3D printing so I will give it a try as my first 3D thing.

[Flump]

OO I could do with a couple of them Zapta as I sometimes work on t cloths and the underside of the boards
snag on it.

let us know how you get on   

[zapta]

OO I could do with a couple of them Zapta as I sometimes work on t cloths and the underside of the boards
snag on it.

let us know how you get on   

I managed today to print one from ABS, it's my first real 3D print. It looks very nice. Just ordered one board from Gerry on ebay, will see how well it will fit.

[zapta]

HI Garry, a question regarding in-circuit resistance change.

Let's say that I have a spare jumper and whenever I want to change a value in one of the columns I first insert the spare jumper in the new location and then remove the jumper from the old location (make-before-break).

Will this give clean transition from the old to the new resistance?

[zapta]

I just posted here a 3D design for a case

http://www.thingiverse.com/thing:521303

Had hard time to print accuratly the snap on version on my gettho 3D printer (Prusa I3V). This design is simple and less sensitive for tolerances. OpenSCAD source code included.

[IanJ]

Nice.......real nice!

I've a 3D printer on order......so guess what I'm printing first!

Ian.

[zapta]

Nice.......real nice!

I've a 3D printer on order......so guess what I'm printing first!

Ian.

This will be a lot of fun ;-)

BTW, possible improvements for this product are more visible jumper color (e.g. red), the black on black is not very visible) and providing an extra jumper for make before break transitions when needed.

[magetoo]

BTW, possible improvements for this product are more visible jumper color (e.g. red), the black on black is not very visible)

Or a different colour solder mask.  I'd like a tasteless yellow one for Christmas, but then of course Fluke's legal team would come knocking on Gerry's door.  :-)

Having a choice of colours could be useful too (the green board is for setting "foo" and the red one for "bar") if there was enough volume to justify it.

[zapta]

Another possible improvement of this product is the order of the 0-9 numbers in each column. Currently moving a jumper up reduces the resistance. Counter intuitive IMO.

[JohanH]

This was a cool little device, so I decided to make one. Old thread, but worth resurrecting.

I documented it here:

https://baldpenguin.blogspot.com/2023/01/programmable-resistor-decade.html

Basically I used more expensive resistors to get it to a rating of 1 W and 0.5 %.

[MarkS]

Forgive my ignorance, but what does this do, how do you use it and how does it help in prototyping?

I've heard of decade resistors, but I'm unclear on their purpose.

[JohanH]

For instance, if you have a circuit where you are adjusting a resistor value, you can use this resistor decade to quickly and very precisely find a value (in the final circuit you would use a normal resistor of course). An alternative is to use a trimmer and measure its resistance afterwards. But trimmers and potentiometers aren't that accurate and can be hard to set to an exact value (works better with a multi turn trimmer). With a more accurate resistor decade you can also verify multimeters. Of course, the point with this design was that it was cheap, so you don't have to be so careful with it. I have a few PCBs, so I might still put together another one from a bag of cheaper SMD resistors.

[MarkS]

For instance, if you have a circuit where you are adjusting a resistor value, you can use this resistor decade to quickly and very precisely find a value (in the final circuit you would use a normal resistor of course). An alternative is to use a trimmer and measure its resistance afterwards. But trimmers and potentiometers aren't that accurate and can be hard to set to an exact value (works better with a multi turn trimmer). With a more accurate resistor decade you can also verify multimeters. Of course, the point with this design was that it was cheap, so you don't have to be so careful with it. I have a few PCBs, so I might still put together another one from a bag of cheaper SMD resistors.

Awesome! Thank you. I bought two.

[Neil_UK]

This could be made somewhat more compact, using a 2x4 header (which has 10 distinct positions where a jumper can be plugged) and 6 resistors (of two values) per decade.

One downside to this layout is that you cannot short the '9' position to keep the resistance finite when moving a jumper - that would result in an incorrect resistance in some positions due to resistors ending up in parallel.

Inspired by the above post, I did some more thinking, and came up with a slight improvement (I think).



In case the improvement is not apparent, it's the fact that the altered resistor order means that the jumpers now proceed down the pin field in consistent increments of 3 per level, rather than switching from side to side. This may simplify the annotation. Or it may not, as the previous arrangement has only odd numbers one side, and evens the other.

I also take issue with Jason's assertion that you cannot leave '9' shorted. Any lower numbered jumper shorts the resistors leading up to node '9', meaning that node 9 has no effect on lower valued jumper positions. Leaving the 9 link shorted has two benefits. It eliminates one layout crossover. It means removing a jumper never gives an open circuit, required in many applications.

As well as these 6 resistor solutions, there are also two 4 resistor networks that can be shorted by a single link to yield all resistance values from 0 to 9, (1,3,3,2) and (1,1,4,3). However these do not share the elegant pin locations and easy jumpering of these 6 resistor solutions, or indeed the 9/10 resistor solution that is the subject of this thread.