Looking for a USB interfaced ohm/resistance meter

kayvee said:
Don't forget PCB origination costs, whichever technology you use.
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Should work out to around R7/unit at this scale, as the setup costs would be around R700 for something of this simplicity and size.
 
Another alternative is to choose a microprocessor that has built in USB capability, like the ATMEGA32U4 that is used in the Teensy (available for $16, possibly less in volume). Add LDR and header pins, and code it up (Arduino compatible), and you are good to go.
 
Man I wish it was 15 years ago when I did firmware for PIC and 8051. Good times.
 
Archer said:
Sigh, I really wish I had gone into electronic design after varsity, this is exactly the kind of stuff I want to be doing, and exactly what I studied :(

One thing to add, no need for analogue data - calibration can be done via a potentiometer. And generally LDRs can vary their resistance quite a bit, so if you only looking for light/dark, calibration should not ever be required.
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Would prefer not to have to hand tune anything, rather have the software figure out the limits.
 
Awesome info guys, had to google several terms, out of touch with this side of the tech world.
 
biometrics said:
Awesome info guys, had to google several terms, out of touch with this side of the tech world.
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Shout/PM if there is anything I can help with. I'm not actively doing embedded software development right now, except on a hobby basis, but still have the resources and such available. I'd be happy to do some coding for you and I know a retired engineer that could whip up a prototype in a day for you, pending availability of parts of course. Anyway, as I said, it's not something I do as a job anymore but I'd be happy to give advice.
 
Messugga said:
Shout/PM if there is anything I can help with. I'm not actively doing embedded software development right now, except on a hobby basis, but still have the resources and such available. I'd be happy to do some coding for you and I know a retired engineer that could whip up a prototype in a day for you, pending availability of parts of course. Anyway, as I said, it's not something I do as a job anymore but I'd be happy to give advice.
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I've read all the comments and I'm wondering, what is the cheapest and easiest way to read a LDR via USB?
 
biometrics said:
I've read all the comments and I'm wondering, what is the cheapest and easiest way to read a LDR via USB?
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Cheapest would be via the launchpad, I believe. $4.30 shipped, however, I don't believe that you could purchase 100 of them so easily.
Next cheapest would probably be the STM32Discovery, although the "license" forbids using them in production.
After that, something like the Teensy is probably closest to what you require. $16 each, add an LDR, a regular resistor and some code and you are sorted.

Here are a couple of pages to illustrate how simple it is:

http://webzone.k3.mah.se/projects/a...rduino_meets_processing/instructions/ldr.html

http://www.libelium.com/squidbee/index.php?title=Adding_a_light_sensor

In truth, the Teensy is probably more powerful than you need, but finding something smaller that still fits the bill might be tricky. Depending on what you need this for, and how many you expect to make if this initial batch goes well, it might well be a better idea to consider things like an ATTiny microprocessor on a custom board.

Example: http://obdev.at/products/vusb/easylogger.html
http://www.uelectronics.info/diy-the-cheapest-dualchannel-scope
http://www.xs4all.nl/~dicks/avr/usbtiny/
 
Archer said:
Let me know of a place (in CT) and I'm there like butter on toast! :D
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Yup, very little, but it's also a scummy industry. Run by dickbutts who will pay you peanuts (in the one interview they literally LOL'd when I said that offers on average for me were 20-22 as a grad and said it would be much less). And these same people will also not give a screw about you as well as the fact that you'll be in the same position for years. Nevermind the fact that it irritates the hell out of them that they have to pay you to do work but also need you because they don't have anyone else they already pay to do it.

Not setting foot in the electronic design industry in SA. Overseas, would love to, but not SA. Too many of these kind of people in it :/
 
UnUnOctium said:
Not setting foot in the electronic design industry in SA. Overseas, would love to, but not SA. Too many of these kind of people in it :/
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That sounds like an overly generalised view on it. Possibly your experience tells you this, but it's also a misinformed one.
 
Isn't there a much simpler way to do this? Connect the LDR to a 555 in such a way that the frequency changes depending on the resistance. Maybe it would then be possible to use this signal to repeatedly trigger the USB port and calculate the frequency/resistance. I don't know much about programming a USB port but this would be simple using a parallel port. You can also buy USB to parallel port adapters for ~R60 which you might be able to use if this is not possible using the USB port directly.

What about using a cheap $5 USB sound card? There is lots of soundcard/oscilloscope software available.
http://www.dealextreme.com/p/usb-3d-sound-adapter-color-assorted-5831
http://www.zelscope.com/
http://www.zeitnitz.de/Christian/scope_en
 
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Yotch said:
Isn't there a much simpler way to do this? Connect the LDR to a 555 in such a way that the frequency changes depending on the resistance.
Click to expand...

Going this route would be ridiculously simple. It would require a fair amount of calibration, however, unless you go for some pretty good quality parts. Connecting it to a USB/RS232 adapter and listening to one of the pins may be the way to go. Hell, if you remove the cover on the serial adapter, you can even make it nice and compact in a little enclosure and also power it off of the USB port.
 
RoganDawes said:
Arduino should have lots of sample code you can use, and for a microprocessor n00b, it would probably be the easiest solution.
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Lol, if you can use a microprocessor then why not? Nothing n00b about not wanting to redesign the wheel.

You can get a PIC microchip that can easily interface with the USB.
 
Messugga said:
Going this route would be ridiculously simple. It would require a fair amount of calibration, however, unless you go for some pretty good quality parts. Connecting it to a USB/RS232 adapter and listening to one of the pins may be the way to go. Hell, if you remove the cover on the serial adapter, you can even make it nice and compact in a little enclosure and also power it off of the USB port.
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Yes the USB to RS232 adapters are even cheaper than the USB to parallel and might be simpler to program. There seems to be an even simpler solution though - a cheap USB webcam. If you use something like this then you don't need to develop any hardware only software and it should be much more flexible/accurate than just one LDR. The Chinese sell these for < $5.

$3 USB to RS232 converter
http://www.dealextreme.com/p/usb-to-rs232-adapter-with-usb-extension-cable-41cm-length-24799
Sub $5 webcam
http://www.dealextreme.com/p/usb-pc-webcam-300k-pixel-with-6-led-13
 
Yotch said:
Isn't there a much simpler way to do this? Connect the LDR to a 555 in such a way that the frequency changes depending on the resistance. Maybe it would then be possible to use this signal to repeatedly trigger the USB port and calculate the frequency/resistance. I don't know much about programming a USB port but this would be simple using a parallel port. You can also buy USB to parallel port adapters for ~R60 which you might be able to use if this is not possible using the USB port directly.

What about using a cheap $5 USB sound card? There is lots of soundcard/oscilloscope software available.
http://www.dealextreme.com/p/usb-3d-sound-adapter-color-assorted-5831
http://www.zelscope.com/
http://www.zeitnitz.de/Christian/scope_en
Click to expand...

Yotch said:
Yes the USB to RS232 adapters are even cheaper than the USB to parallel and might be simpler to program. There seems to be an even simpler solution though - a cheap USB webcam. If you use something like this then you don't need to develop any hardware only software and it should be much more flexible/accurate than just one LDR. The Chinese sell these for < $5.

$3 USB to RS232 converter
http://www.dealextreme.com/p/usb-to-rs232-adapter-with-usb-extension-cable-41cm-length-24799
Sub $5 webcam
http://www.dealextreme.com/p/usb-pc-webcam-300k-pixel-with-6-led-13
Click to expand...

Brilliant thinking outside the box.
 
You can rather just get a voltage-to-frequency chip instead of a 555, it will be more accurate...
 
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