RTD Simulator using dip switches and SMD resistors or basic decade box!!!

by on Feb.22, 2015, under Electronic Projects

Decade box (RTD Simultator) using dip switched and SMD resistors.

To start off I did not come up with this idea.

(Search on Hackaday dot com or Thinkcreate).

I work in a world of instrumentation and we have field techs who do not like to return shiny expensive equipment when they leave our employment, so came up with a cheaper and less shiny looking device and may be they will not want to take it as there own.

This is the schematic:

decade box smd


Very basic but brilliant design. If you take 1,2, and two 3 ohm resistors you can make each value between 0-9 ohms. Just increase each back by x10 to create your decade box.

For me I started at 0.1,0.2 and 0.3. I wanted to build RTD simulator.(This also creates a 999.9 ohm Decade box)

Now I tried a new PCB maker. Dirtypcbs.com. They have a 5cm x 5cm board size $14.00 with free shipping. (Took 1 month receive my boards from the China)

They say you may get 10 boards or less or more, I got lucky and got 12. Should have bought a lottery ticket that day… 🙂

They came in a nice little box and shrink wrapped like this:


I am a cheap bastard and like to get the most for my money, so I put two decade units on my main board to use up the 5cm x 5cm board.



My thoughts was to cut them into separate boards, but then came up with a better idea.  Make a high and low side for testing the span on the transmitters we work with.

Also if you want to create a full decade box you could by daisy chaining the two units on the board to give you 8 x10 ranges like below.

Dip 1=.9 ohms, dip 2=9 ohms, dip 3=90 ohms, dip 4=900 ohms, dip 4=9 kohms, dip 5=90 kohms, dip 6=900 kohms, dip 7= 9 mohms and dip 8=90 mohms. (99999999.9 ohms)

Or adjust the resistor values to your requirements. (Try to use 0.1 to 0.5 % resistors for the lower ranges, and 1% for the higher)

My Dual range RTD Simulator:

IMG_8714 IMG_8715 IMG_8713


You can purchase boards from Dirtypcbs.com using this link:




All resistors are 0805 SMD

My Digikey order per Side (double your order for a dual range unit):

1   CRL0805-FW-R100ELFCT-ND .1 ohm resistor 805 R1
1   CRL0805-FW-R200ELFCT-ND .2 ohm resistor 805 R2
2   CRL0805-FW-R300ELFCT-ND .3 ohm resistor 805 R3/R4

1   311-1.00CRCT-ND 1 ohm resistor 805 R5
1   311-2.00CRCT-ND 2 ohm resistor 805 R6
2   311-3.00CRCT-ND 3 ohm resistor 805 R7/R7

1   311-10.0CRCT-ND 10 ohm resistor 805 R8
1   311-20.0CRCT-ND 20 ohm resistor 805 R9
2   311-30.0CRCT-ND 30 ohm resistor 805 R10/R11

1   CR0805-FX-1000ELFCT-ND 100 ohm resistor 805 R12
1   CR0805-FX-2000ELFCT-ND 200 ohm resistor 805 R13
2   CR0805-FX-3000ELFCT-ND 300 ohm resistor 805 R14/R15

4   GH7170-ND 4 position rocker switch SW1/2/3/4

1   WM4393-ND Terminal dual X1


I would recommend a Gold contact switch if you are decide to make the dual range unit. (Digikey part 360-1181-ND)

I am very pleased on how this proof of concept project turned out. I also hope it helps you on one of your projects.

Till next time, Thanks for your time.











2 Comments for this entry

Leave a Reply

You must be logged in to post a comment.

Looking for something?

Use the form below to search the site:

Still not finding what you're looking for? Drop a comment on a post or contact us so we can take care of it!

Visit our friends!

A few highly recommended friends...