Alt-BEAM Archive

Message #11946



To: alt-beam@egroups.com, BEAM beam@sgiblab.sgi.com
From: David Simmons devs@idirect.com
Date: Thu, 16 Mar 2000 00:45:53 -0800
Subject: [alt-beam] Re: FRED bread boarded...problems


One of the cheaper, and better SE's around. My son is working on the
photopopper right now--breadboarded it tonight and in the morning we
start putting it all together. He has already decided on a name "Freddy
Jr."

Regards,
Dave

Ben Hitchcock wrote:
>
> Hi,
>
> For those of you not familiar with the FRED solar engine, check out
> http://wollongong.apana.org.au/~ben/fred/schematic.html. It's a solar
> engine that can make a photopopper out of some pretty cheap components. I
> used a slightly modified version in my seaplane (linked from that page).
>
> > Is it possible to make some componenet changes in the FRED design. Have
> > a
> > 4700uf cap and 2.2k resistors instead of 4.7uf cap and 3.3 resistors?
>
> It is possible to make lots of changes to the FRED circuit and still have
> it working fine. Some changes might even improve performance. The onyl
> way to tell is to actually try it.
>
> 2.2k resistors will increase the lowest light level that FRED will work
> in, and raise the switch-on voltage slightly, but it should work.
>
> 4700 uF is way too high. The idea is that this cap is low enough to
> charge up very quickly - otherwise there isn't much point making a FRED, a
> standard FLED SE will do the same job. Use something small such as a 0.22
> uF cap or 0.1 or so. You might have some of thse lying around drom a
> microcore project.
>
> > I
> just bread-boarded FRED but it didn't work. The FLED would flash but the
> > motor would not turn. I only bread-boarded half the circuit, or one engine.
> > I don't know why this is. Where does the second wire of the FLED go? Any
> > help would be appreciated.
>
> What values are you using? Are you using a 33k resistor to bias the FLED?
> If so the FLED should be very faint. Is your cap (4.7 uF) around the
> right way? If you're using a 4700 uF cap then this is your problem.
>
> > Also...
> >
> > If I use a larger voltage than something like a 2 or 3 volt solar panel, do
> > I need a larger cap?
>
> The FRED design will turn on at about 2.4 volts so no matter how high your
> solar panel voltage is, it will never get there.
>
> I used a calculator solar panel on my seaplane robot (See the FRED page
> for a link to it).
>
> hope this helps,
>
> Ben
>
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11947 Thu, 16 Mar 2000 01:07:48 -0800 [alt-beam] Current draw of DC Motors BEAM , alt-beam@egroups.com David Simmons Hey all,

I was out today with my son looking to upgrade his Multi-Meter--His
first was one I had to pick up on the quick several years ago when I was
working on a site out of town and had to debug a new CNC machine being
installed over the phone with a tech in Austria.

All we really wanted was something that would show Current draw on a DC
motor, that seems to be the only feature his current meter is lacking.
The salesman was very willing to show us a range of meters from $20.00
to well over $200.00 but once we got talking he told me a little way
around the meter problem without any need to up grade the meter.

He said to place a 10 ohm 10 watt power resistor between the plus
termianl and the motor. Measure the voltage across the resistor and use
Ohm's law to find the current.

I = E/R

Thus 1.21 volts across the resistor would be:
I = 1.21 / 10
I = .121 Amps or 121 mA

Is this correct? Or am I way out to lunch here?

Thank you,
Dave

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