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M, Thanks for this info. Its for a piece of test equipment and the sensor measures a voltage which will range between -30V & +30V DC which I want to read in Hyperterminal on the computer. I'm wanting to measure in increments of milli volts. Ideally am looking for a product that can do this alternatively if the MAX232 IC will do what I want then I can look at building a PCB.
You could get a data acquisition card or USB connected board which would be able to read analog voltages. The ±30V range would need to be scaled down most likely.
Here is an example:
http://www.dataq.com/data-acquisition/usb/?source=googlesda&gclid=CJOQyKvbtccCFVU6gQodagkNfQ
A unit for just $29 will read up to 4 analog voltages ±10V. All you would need is 2 resistors in a voltage divider to convert your range to that range.
Bob
Here is an example:
http://www.dataq.com/data-acquisition/usb/?source=googlesda&gclid=CJOQyKvbtccCFVU6gQodagkNfQ
A unit for just $29 will read up to 4 analog voltages ±10V. All you would need is 2 resistors in a voltage divider to convert your range to that range.
Bob
hevans1944
Hop - AC8NS
@Steve_O One millivolt resolution in a 60 volt span means you need at least a 16-bit analog-to-digital converter. Adding ancient RS-232 communications protocol increases the cost somewhat compared to a USB solution. Try this web page for a 16-bit A/D with RS-232 communications protocol.
If you choose the product cited on the web page, you will need to attenuate and then offset your ±30 VDC signal to accommodate the 0 to 2.5 V input range of their A/D. In other words, a 1:24 attenuation followed by a precision +1.25 V offset will do the job. Thus a -30 V input becomes -1.25 V, which then becomes 0 V after offsetting by +1.25 V. The +30 V input becomes +1.25 V, which then becomes 2.5 V after offsetting by +1.25 V. The A/D output then varies from 0x0000 to 0xFFFF as the input varies from -30 V to +30 V.
You should build a small circuit board containing buffer operational amplifiers and an IC-based precision voltage source to perform the analog signal attenuation and offset signal conditioning described above. Be sure to mount the circuit board inside a shielded metal enclosure to avoid noise pick-up. If at all possible, use precision resistors to perform the attenuation and to scale the offset voltage. Avoid using trim potentiometers if possible because they will introduce temperature-induced drift as well as noise from their wiper contacts. If a trim pot is unavoidable, its value should be in the range of one to ten percent of the value of the resistance you are trimming. That is, a 100 ohm trimpot is appropriate for trimming a 10 kΩ resistor, but a 1 kΩ trimpot is pushing your luck.
If you are comfortable rolling your own hardware and software, there are many A/D solutions that can be integrated with a microcontroller that implements an RS-232 interface. This would possibly be a "fun" project, but an off-the-shelf solution is probably a better idea.
If you choose the product cited on the web page, you will need to attenuate and then offset your ±30 VDC signal to accommodate the 0 to 2.5 V input range of their A/D. In other words, a 1:24 attenuation followed by a precision +1.25 V offset will do the job. Thus a -30 V input becomes -1.25 V, which then becomes 0 V after offsetting by +1.25 V. The +30 V input becomes +1.25 V, which then becomes 2.5 V after offsetting by +1.25 V. The A/D output then varies from 0x0000 to 0xFFFF as the input varies from -30 V to +30 V.
You should build a small circuit board containing buffer operational amplifiers and an IC-based precision voltage source to perform the analog signal attenuation and offset signal conditioning described above. Be sure to mount the circuit board inside a shielded metal enclosure to avoid noise pick-up. If at all possible, use precision resistors to perform the attenuation and to scale the offset voltage. Avoid using trim potentiometers if possible because they will introduce temperature-induced drift as well as noise from their wiper contacts. If a trim pot is unavoidable, its value should be in the range of one to ten percent of the value of the resistance you are trimming. That is, a 100 ohm trimpot is appropriate for trimming a 10 kΩ resistor, but a 1 kΩ trimpot is pushing your luck.
If you are comfortable rolling your own hardware and software, there are many A/D solutions that can be integrated with a microcontroller that implements an RS-232 interface. This would possibly be a "fun" project, but an off-the-shelf solution is probably a better idea.
Last edited:
hevans1944
Hop - AC8NS
Besides wanting to measure -30 V DC to +30 V DC with a resolution of one millivolt, how fast do you want to make these measurements? A few thousand samples per second is probably feasible with a fast RS-232 baud rate, but limiting it to a few hundred samples per second (or less) will prevent a lot of headaches and the A/D will cost less. For example, a delta-sigma converter (MCP3424) from Microchip will do 16-bit conversions at about fifteen samples per second and costs about US$4.00. However, it requires a lot of support circuitry and software to make it do anything useful.
So, how fast do you need to take samples, and what baud rate do you want the RS-232 link to run?
Is this what you may be looking for ?
ADAM 4017 DATA AQUISITION MODULE
http://www2.advantech.com/products/GF-5VTD/ADAM-4017+/mod_10FD9E9C-8E8A-42F2-B749-A395F8426262.aspx
Man i had like 10 of theese and i sold them for 50 bucks each. Theese things cost a fortune to buy new.
ADAM 4017 DATA AQUISITION MODULE
http://www2.advantech.com/products/GF-5VTD/ADAM-4017+/mod_10FD9E9C-8E8A-42F2-B749-A395F8426262.aspx
Man i had like 10 of theese and i sold them for 50 bucks each. Theese things cost a fortune to buy new.
