Hi, 

I want to be able to automatically measure how much my rat eats in a
given hour and log it to my PC.  I do not have a lot of money to spend
on this- it has to be below $200 US dollars.   I have an idea so far
as to how to do this (shown below Appendix A) and would not mind if
the answers were base around it.  The food basically would be hanging
on some kind of device that can log down the weight of food at any
given moment.

My question to all the experts out there is this: 

Can anyone provide me with a diagram of how to set this for under 200
dollars?  This diagram should be drawn so that a person without any
knowledge of electronics can build one –
(I emphasized on the without “knowledge of electronics” part).   The
diagram should also come with detail instructions.  Hopefully I can
just look at this diagram and build my device right away without
trouble. Oh and please let me know where one can buy the devices.

Thank you in advance.   

--- Appendix A

So far this is what I know.  I know that Picotech has this device call
the ACD16, which accepts different voltage inputs and transmits it to
a PC.

http://www.picotech.com/data.html#adc16

they also have a device call a load cell (SE022), which supposedly can
change resistance according to how much tension it receives, thus
allowing one to convert it to load (weight).

http://www.picotech.com/accessories/load_cells.html

Everything looks great, but the problem is that the device requires a
regular 10V supply (which I cannot find anywhere) AND worse, does not
come with detail instruction as to how to build something like this.

Hello,

You may be interested in scales which already have a computer hardware
linkup already built into them. RS232 (stanard serial port)
connections come with almost every Ohaus balance. The 2nd half of
grabbing the data is processing it and figuring out what to do with
it. Ohaus, the largest laboratory equipment manufacturer, is actually
offering a $395 value pack-in by throwing in a copy of their "Balance
Talk" software with every balance purchase. The Explorer series is the
most affordable, and assuming you'll keep a half kilo of food on the
scale while you're feeding it, you'll want the Explorer E14130. These
are professional balances though and will cost you a pretty penny (in
the upwards of $1500). There are cheaper alternatives from ohaus, and
their Scout II line is right up your alley! The SR4010 Scout II
Balance has the RS232 interface for your computer and weighs in at
just under $200 at a retailer which is listed below. You would have to
buy the software separately though, and that will run you $395. There
is however freeware software called which may work with the scale, and
I haven't found any info to suggest that it wouldn't work. So $192 for
the scale, and some for the shipping, and you're set to go all for
around $200. Enjoy!


Additional Links:

Balanace Talk Promotion Info:
http://www.ohaus.com/whatsnew/promotions/baltalk.asp

Balance Talk Pricing:
http://balanceinfo.com/btalk.htm

SR4010 Product Info:
http://www.ohaus.com/products/glo/scripts/view/viewproduct.asp?Recno=SR4010

SR4010 Pricing:
http://balance.balances.com/scales/267

WinCT Data Accumulation Software With Links To Download:
http://www.scalenet.com/and/download.html


Search Strategy:

laboratory equipment balances rs232:
://www.google.com/search?q=laboratory+equipment+balances+rs232


Hope my answer helps,
skermit-ga

First off, are you trying to measure the food consumed during the
total period of one hour, or rather the food consumed during a longer
period with measurements taken hourly? I ask this because your
instrument for measuring mass would have to be more accurate given the
shorter time interval.

That said, remember that building a custom scale would require
calibration using a range of known masses.

Regarding your power supply, a doorbell or buzzer power source could
be the perfect 120v to 10v transformer. But you're not that desperate
yet. It seems that the load cells are different from the other
Picotech sensors in that they require "An additional precision 10V
power supply." Yeesh! However, the ADC-16 that is recommended for use
with the load cells is stated to provide, "Outputs (that) can be used
to directly power sensors." The outputs are 5 volts per terminal
board. If you buy another terminal board ($22), you can use both
outputs to get 10v.

It took me an hour to figure out what they were saying, and I am not
being paid to answer this. Oh, Picotech and your cryptic information!

A cheaper, albeit less accurate, alternative (aside from the doorbell
transformer) may be to use a linear potentiometer in combination with
a spring. In this setup, as mass is relieved from a dish by your rat,
the spring will expand the distance between the platform and the dish.
This distance is then detected by the potentiometer. Of course,
oscillation of the spring could be a problem, especially with a rat
bumping the dish.

The combination of a potentiometer and a spring is actually the same
as a bona-fide force sensor. If you wish to skip the construction and
buy a force sensor, try a Honeywell force sensor at:
http://content.honeywell.com/sensing/prodinfo/force/

Picotech uses a Honeywell for a collision experiment; therefore it
should be compatible. The 500g unit works on 5volts, so you would only
need the one terminal board that comes packaged with the Picotech data
logger.
http://www.picotech.com/experiments/impact_forces/index.html

In response to polypuga-ga: 

Hi, thanks for the wonderful comments.  The last "Researcher" totally
missed the point.

>First off, are you trying to measure the food consumed during the
>total period of one hour

Sort of--but what I really want is the acuire the data constantly
throughout the entire hour.  For example in 5 minutes intervals.

Oh and thanks for the link to picotech:  using the honeywell
transducer is a pretty good idea.  However, the instruction is a
little cryptic and I am worry abot the spring getting loose over time
or worse-- loosing consistency due to the constant load it has to
carry.

Anyways, thanks for the comment. You should apply as a researcher.  

Alex ;)