Bristol Digest, Vol 539, Issue 9

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Today's Topics:

1. Re: Opamp - somewhat off topic (John Honniball)
2. Re: Opamp - somewhat off topic (John Honniball)


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Message: 1
Date: Tue, 25 Feb 2014 20:23:12 +0000
From: John Honniball <coredump@gifford.co.uk>
To: andrew@1dtv.com, Bristol and Bath Linux User Group
<bristol@mailman.lug.org.uk>
Subject: Re: [bristol] Opamp - somewhat off topic
Message-ID: <530CFBB0.301@gifford.co.uk>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 24/02/2014 18:23, Andrew wrote:
> Is there such a thing as 4 or 5 of these on a board, or even 10? We are
> thinking of setting it up to do several in parallel.

The LM324 is a quad op-amp chip. Four separate op-amps in one package.

But from the sound of the discussion, it seems like you need to consult
an electronic engineer before you go much further. If the load-cell
output is as small as you say it is, you may need to take precautions
against noise, and make a circuit that's stable against drift (with
temperature changes, for instance). I've looked at strain-gauge
circuits for small (kitchen) weighing scales, and they use a special
type of differential amplifier called an instrumentation amplifier.
Again, you can buy those in chip form.

An engineer would be able to advise you on accuracy and repeatability
of the circuit. But you'll need to be able to answer technical questions
about the performance of the circuit (numerically).

If you'd like informal advice, may I suggest that you bring the circuit
along to the Bristol Hackspace open evening? We're at 37 Philip Street
in Bedminster (across the road from the big ASDA). Open evening starts
at 7pm on Thursdays.

--
John Honniball




------------------------------

Message: 2
Date: Tue, 25 Feb 2014 22:14:05 +0000
From: John Honniball <coredump@gifford.co.uk>
To: Bristol and Bath Linux User Group <bristol@mailman.lug.org.uk>
Subject: Re: [bristol] Opamp - somewhat off topic
Message-ID: <530D15AD.3070000@gifford.co.uk>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 25/02/2014 19:04, david wrote:
> I am coming a bit late to this conversation, but the Raspberry does not
> have an analogue to digital input.

Oops, that I didn't know!

> ( I am sure I have got some 40 year old 741's around here somewhere )

Extra geek points if they're in the round metal cans!

--
John Honniball




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End of Bristol Digest, Vol 539, Issue 9
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