weird weird question

[Sic]

Ok, so i'm building Dean Hazelwanter's Loopy using an ISA1420 chip... i have it working... sort of...

i'm not concerned about the noise atm, but more concerned about the switching.

I had the record/play on one momentary switch... push down and hold to record... let up to play.

pushing down to record would work... but when i let up... nothing...

i took out the switch, tested it with a DMM and its fine...

re-hooked it up... and then after i recorded i banged the switch on accident...

It worked...

hrm i thought...

so i tried another switch...

then another...

tried a dpdt with seperate ground wires...

same issue...

now... i take the play wire off completely...

after i record... i have to touch the play to ground... remove it, and touch it to ground again... and then it plays and loops...

i hooked the switch back up...

everytime after i record if i give it a little bang it works...

i have NO idea why it would be doing this.

**clueless**

[pjwhite]

I'm not familiar with the circuit, but it sounds like a floating input problem.  Maybe a pullup resistor on the chip input pin is required?

[Sic]

The Schematic/Layout is found at GGG

Floating input? never heard of that, lemme do a Google Search for it and see what i can come up with.

Btw, i see you live in AZ =D me too

[Sic]

wow, ok

Here is an atricle about Floating Input Makes some sense, i need to re-read it a bit tho.

This says that 10k... using the 5v should be enough... and for even better battery saving power use a 47k... would there be a difference in the function changing the value? obviously i want to save as much power as possible.

thanks a bunch for your info pjwhite... this forum is great =D

[pjwhite]

I had a look at the Loopy schematic, and I see that there is a 47K pullup resistor that appears to be connected to: U1 pins 4, 9, 10 and 27, U2 pins 12 and 13, U2 pin 1and the PLAY/RECORD switch.  The schematic is badly drawn (no dots at connecting intersections), so it's not entirely clear that all these points are to be connected together, but I think that's what should be going on.  You might want to check all these connections and make sure the resistor is actually connected to the switch and all the input pins.

As for pullup resistor values and power consumption, a pullup resistor only draws significant current when the switch is closed, grounding one end of the resistor.  On a 5 volt power supply with a 47k resistor this is about 100 microamps -- not very significant, really.  When the switch is open, and the digital inputs go high, the current is much smaller and will vary depending on the number of inputs connected and the type of IC (CMOS, NMOS, etc).
Lower resistor values are used when noise is a problem, or when high speed switching is required.  In this circuit, you could use anything from 4.7k to 100k probably, without a problem.