Electronics > Projects, Designs, and Technical Stuff

A SCPI Programmable (Precision) Resistor

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--- Quote from: SebastianH on September 11, 2023, 03:09:36 pm ---
--- Quote from: Doctorandus_P on September 07, 2023, 01:38:49 pm ---Another part I am always interested in is the global build up of cost and time sunk into a project.

--- End quote ---

The following are very rough estimates. I didn't necessarily pay that much for this project specifically, because I had many parts left from other projects. When bought new the case is likely much, much more expensive than what is accounted for. For some of the parts like the PCBs there is a minimum order quantity that will slightly increase the cost in most DIY scenarios where you simply don't build that many units.

Mechanical parts (including case, panels, connectors etc.): 80 EUR
Mainboard (including PCB, main controller, relays, precision resistors etc.): 176,50 EUR
UI board (including PCB, ui controller, LED displays, rotary encoder, switch, buzzer etc.): 78,50 EUR
Power supply board (including PCB, power switch, AC/DC converter, DC/DC converter): 34,00 EUR

Total: 369 EUR. Pretty expensive, actually.

--- End quote ---

Hi Sebastian,

have you considered making these and selling them ?

I'd be interested !



--- Quote from: Tigerwoods on September 26, 2023, 04:04:45 pm ---Nice work.

As an engineer who's been studing in this field for a while (indeed our team have launched a Kickstarter campaign last year for our QR10 programmable resistance box https://www.eastwood.tech/en/ - which can achieve 0.1 ohm steps and up to ±0.01% reading accuracy), you need to solve two major problems if you want to make it more precision:

1. Forget about the ideal formula (it's simple if you ignore the relay's contact resistance and choose strict 2^n valuse to achieve 1% or 0.2% overall accuacy)

2. Find a smart way for calibration (time-consuming measurements can work, but it may not work so well for high accuracy)

At last, you should be careful to select the switches.

Good luck!

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Can it be controlled via LAN and SCPI ?

Thank you,

It has a USB port (actually it's USB-COM that presents as a COM port on your PC). You can use simple command like "AT+SP=123.4" to set it output 123.x Ω


--- Quote from: Tigerwoods on September 26, 2023, 04:04:45 pm ---At last, you should be careful to select the switches.

--- End quote ---

Which relays did you choose?

--- Quote from: luudee on September 26, 2023, 05:10:07 pm ---have you considered making these and selling them ?

--- End quote ---

No, it's not worth it for me. But if you want to build something like this yourself, most relevant parts like schematics and firmware for the main controller are open source (currently minus the UI board firmware). See my github account.

Looks great. Definetly will put this on my long list of things i want to build. Probably needs some modifications to bring the cost down to be more in my price range


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