Re: trimpot
- From: John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 08 Feb 2008 08:53:31 -0600
On Fri, 8 Feb 2008 04:04:38 -0800 (PST), bill.sloman@xxxxxxxx wrote:
On Feb 8, 9:51 am, jchan...@xxxxxxxxxxx wrote:
I hope I do not sound stupid. I am good at soldering kits together
but do not understand all what is going on with the electronics. I
have a 5 led random/sequencer flasher kit I purchased and built. It
works good but I want to slow the flash rate down quite a bit. I know
the trimpot controls the speed so is it as simple as putting in a
different trimpot? If so, how do I figure out which one? The
schematic of the kit can be found athttp://www.kitsrus.com/pdf/k52.pdf
The kit doesn't identify the integrated circuit that contains the
oscillator and controls the LEDs.
It is probably some kind of CMOS chip - the Vss label on the circuit
diagram suggets as much - but you are going to have to take a close
look at the chip to see if you can see some kind of part number on it
before we could be all that much help.
---
That seems highly unlikely in that the first sentence in the link:
"This cmos VLSI single chip-on-board is designed for
electronic toy and warning light applications."
identifies "chip-on-board" (COB) as the means used to affix the chip
to the board.
In that method of construction the bare die is affixed to the traces
on the PCB and then covered over with a dollop of epoxy in order to
protect it mechanically and environmentally.
Consequently, there is usually no way to identify the chip or its
internal circuitry.
---
The situation doesn't look promising. If there was an explicit
capacitor on the schematic, it would be easy enough to replace it with
a higher-capacitance part which should then give a lower the
oscillator frequency. The absence of an explicit external capacitor
suugests that the circuit might rely on an internal capacitor,
possibly part of the integrated circuit, which you wouldn't be able to
get at.
A higher value potentiometer might lower the operating frequency, but
all the potnetiomenter ranges I know stop at 1M so this isn't a
practicable option.
---
Don't get around much any more, huh?
They seem to be as common as dirt:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=262968;keywords=potentiometer
http://www.mouser.com/search/Refine.aspx?Ne=254360+1447464&N=254360+1323038&Ns=P_SField
Besides, if he's not looking for being able to vary the flash rate
he can simply replace the rheostat with a fixed resistor.
Assuming, of course, that the value of the resistance doesn't exceed
whatever might be the chip's limitation.
Easy way for him to find out is to try it.
--
JF
.
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