Interesting chips

Paul Baker

I am using this chip in a prototype (though I most likely won't use it in the final design), but it's interesting enough to share. It's actually·2 chips from New Japan Radio (NJR aka JRC) the·NJU7312 and NJU7313. These are analog switches but are configured in interesting ways. They are configured as a 4xSP3T·+ 2xSPDT, and a 2xSP4T·+ 4xSPDT respectively. While thats not really impressive, it appears any branch can be connected to the pole at any time. By connecting different switches together you can create complex communication bridges.·Also the interface is 2 wire SPI and one of each chip can share the same bus, though it's top speed is 100kbps and 14 bit packets (update 8 of the 16 branches a little over 7000 times a second) so it's not good for high speed switching. The datasheet is a little light on some·information (such as channel capacitance), so I'll have to test it.·Mouser stocks the parts.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

mosquito56

Could I use these to connect multiple voltages to single 0831 chip? I want to connect multiple sensors to the 0831. The 0831 only has 8 inputs. To increase the pins would this work or should I use an I2C register? As I know nothing about I/0 expansion, the dpst switches seem like a good way to connect multiple outputs to 1 input.

Thanx

Also, are they avail at mouser or any American Company?

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······· "What do you mean, it doesn't have any tubes?"
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Paul Baker

I don't know what a 0831 is, whether it would work depends on a variety of factor which can't be answered unless I know what the chip is.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

LoopyByteloose

Are these telephone switching chips? William Chan would be interested.

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PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

mosquito56

Sorry, I may have typed the wrong number. Should be ADC0831.

I really want to connect multiple inputs to a single op-amp then to the ADC.

I know nothing about i/0 expanders but from what I read they would be digital expanders and I need an analog expander.

Thanx

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······· "What do you mean, it doesn't have any tubes?"
······· "No such thing as a dumb question" unless it's on the internet
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sam_sam_sam

mosquito56

This maybe what you are looking for

http://atic.phys.lsu.edu/aces/Docs/Component%20Docs/adc0831.pdf

Now can you use the Demo Code that is for the ADC 0831 on a

ADC0832 2-Channel MUX..·or ...·ADC0832 4-Channel MUX·..or
.. ADC0832 8-Channel MUX....... I do not know......>
All·I can tell you is about the ADC 0831·which·I·have only played with
I·have not try these other ·chip yet but i will
I will need a 2-Channel· for something that i am working on




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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 2/28/2008 9:29:02 PM GMT

mosquito56

· I already have a maxium 1270 which is an 8 channel ADC. The problem is that I am using thermoucouples which each require an op-amp to bring the small mv value up to a value the adc can use.

I want to avoid the multiple op-amps and just run 12 wires to a chip to the op-amp. When I get to 12 op-amps, I am afraid of noise and temperature variations that will kill me in terms of accuracy. With one op-amp, I can calibrate each channel thru software.

That is why I am looking for a simple switching device to go from one thermocouple to the next. Since I have only been back into electronics for about 2 months, I have no idea what they would be called.

Think of a simple rotary dial. I rotate and change inputs. I want to do this rotation electronically but have no idea what it would be called but the chip Paul suggests seems to be what I am looking for.

· I looked at the datasheet and it's Japanese to me.

Thanx




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······· "What do you mean, it doesn't have any tubes?"
······· "No such thing as a dumb question" unless it's on the internet


Post Edited (mosquito56) : 2/28/2008 9:42:19 PM GMT

Paul Baker

Yes if you use the op amp in non-inverting configuration it should work just fine. If you are using it in inverting mode you need to add the ~200 Ohm channel resistance in your calculations of Ra to obtain the correct gain.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

mosquito56

Paul, I already have the system working but only one·input. My question is can I use the chips you mentioned in·original post to hook up multiple·thermocouples. Is the chip you mentioned an analog device or a digital device?
· You mentioned 4spdt. Switches I can understand but will they pass a voltage staight across or are they only for digital info? I.E. Hi,low?
· If it's digital, is there any such thing as an electronic "rotary" switch?

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······· "What do you mean, it doesn't have any tubes?"
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MikeK

The datasheet is the place to look for such information. It is an analog switch. It has an ON resistance of 100 ohms if I remember correctly.

stevenmess2004

mosquito, it may be better to use a small reed relay. Almost no resistance that way.

Mike Green

Unfortunately, you need to measure very low voltages from the thermocouples. Any electronic switch you put between the thermocouple and the op-amp is going to introduce noise and offset voltages. Reed relays may be the best choice. They're not as fast as an electronic switch, but they're pretty fast and they won't introduce much noise or offset if you're careful about how you mount them and route the signals from the thermocouples and shield the whole thing up through the point where the signals are amplified.

Mike Green

If you really need to use a semiconductor solution, you might consider using two 8-input 16-bit ADCs. These often have a 4.096V internal reference and, with a 16-bit resolution, could give you values from 0 to 1023 over a 0 to 63mV range. Again, you'd have to be very careful about layout and power supply filtering to avoid introducing noise or offset voltages, but it is another potential solution.

mosquito56

What is a reed relay?, never heard of it, wiki time.

·Mike, what kind of adc can read 0 to 63mv? Everything I've read on thermoucouples has shown an op-amp to boost the voltage up to the normal 0-5V range. I am normally wrong.

· Most thermocouple modules are expensive. The maximum is $7.65 each up to a 100 qty.It is a k thermocouple specific chip and has the op-amp built in. ·The parallax module is $32 for a 3 channel I think module. Needing 12 wires starts getting expensive, but since the aircraft engine cost me $20,000 a couple hundered extra is not a problem. I don't plan to start the engine for a couple more months so I will just take it one step at a time.

·Right now I have one k thermoucouple wired to an op-amp to a adc0831. It seems to be working but I haven't ordered the temp gun yet to calibrate it. Hope I can get by without a lookup table. ·Someone suggested a couple months ago to get the ·max1270, it has 8 adc inputs. That is my next project.

Thanx for the input. This digital stuff is so new to me it's unreal.

Darn, I just realized I have hijacked Paul's thread, sorry about that Paul.

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······· "What do you mean, it doesn't have any tubes?"
······· "No such thing as a dumb question" unless it's on the internet
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