how to use multi-channel ADC with a BS2 ?

Aaqil Khan

Hi everyone,

I want to design a circuit to measure various parameters of a transformer (voltages, load currents and temperatures).
Using suitable sensors, I want to know how to design a circuit to read the converted analog voltages using a basic stamp (BS2PX24). My intended design looks like this:

(SENSOR) ---> [noparse][[/noparse]AMPLIFIER & FILTER STAGE]

---

> [noparse][[/noparse]MULTI-CHANNEL ADC] ---> (MICROCONTROLLER).

What i want to know is:
1. how to design the amplifier and filter stage (assuming electrical noise from transformer humming)?
2. how to select a multichannel ADC?
3. how can i program a basic stamp to tell the ADC to cycle thru the various sensor inputs? (the only ADC i've used is the single input ADC0831 !!!)

I appreciate all the help.

Thanks,
<EDIT> Title added by moderator </EDIT>

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E=mc^2

Post Edited (Aaqil Khan) : 1/10/2007 2:41:06 AM GMT

Steel

Are you asking us to design your project?

I can help you...but Im not free.

Aaqil Khan

hi steel,

thanks for your reply.

i would appreciate if you could tell me what factors do i need to consider to design the filtering components?

And how to interface a multichannel ADC with a basic stamp? I mean, how can i read say, 8 sensor outputs with 1 ADC and what do i need to consider while selecting an ADC (other than resolution and number of channels).

Thanks in advance.

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E=mc^2

Chris Savage

Aaqil,

We have an 8 channel ADC on our website. Besides resolution and number of channels you should also be concerned with input voltage range and reference/span adjustment. Input voltage range on most ADC chips is 0 – 5V. Being able to set the voltage reference could help if your input voltage is substantially less than 5V (or maximum input voltage).

Say you only need to measure 0 – 1V. If you cannot set the voltage reference down to 1V then you will waste a good portion of the resolution on voltages you won’t be measuring whereas if you set the voltage reference to 1V the complete range of the ADC is available for that signal. I hope this helps. Take care.

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Chris Savage
Parallax Tech Support

Aaqil Khan

Thanks for your reply Chris.

Two·more questions:

1. can you send me the link for that 8-Ch ADC? I could only find a 4-Ch ADC on your website.

2. In using the 8-Ch ADC, since there is only 1 digitized output, how does the BS2 know·and control the various analog input channels? Does it cycle through Ch0 to Ch7?
I've never used a multi-channel ADC before. I pretty much understand single channel ADCs (thanks to the ADC0831)

I'd appreciate if you could shed some more·light on this topic.
Thanks in advance.

Aaqil

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E=mc^2

Chris Savage

Aaqil,

·· The 8-channel ADC we have can be found at the link below. As a side-note, there is the ADC0831 (single channel) and ADC0834 (4-channel) and although we don’t carry there is an ADC0838 (8-channel version) that is very similar in control format. As for the multiple channels, these devices are generally SPI or I2C interface and you send a command to select the channel. An internal MUX switch the input to the ADC hardware so you can read the result. You can find this information in the datasheet for almost any ADC chip. I hope this helps. Take care.

http://www.parallax.com/detail.asp?product_id=604-00026

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Chris Savage
Parallax Tech Support