(Idiot alert) Millenium Bypass and Pull Down Resistor

[johnadon]

I've used the Millenium 2 bypass with mosfet /ordinary transistor on about 15 projects thus far. All have worked fine except for two where I've run into a problem with the LED staying on all the time whether or not the effect is bypassed or engaged. I've fixed this problem on both by adding a 100K to 1M resistor from the board effect output to ground. This pretty much puts another resistor in parallel with the existing output pulldown resistor doesn't it, merely decreasing the pulldown resistance? (Both circuits had existing 1 meg pulldown resistors.) I can't figure out why this fixes the problem although I think I had a fuzzy idea at one point or I wouldn't have tried it. One of them wouldn't function properly until I went all the way down to a 100K resistor from board output to ground.

Is there a better way to avoid this issue in the future? I'm wondering if changing the current limiting resistor coming off Millenium 2 LED will fix the problem a bit more elegantly? I noticed on R.G. Keen's graphic of the Millenium 2 (http://www.geofex.com/Article_Folders/Millenium/milckt.gif) that he specifies a range of values for the current limiting resistor from 1K to 4.7K, hence my question. I'm not sure if the range was just to accomodate varying tastes in the brightness of an LED or if it has another function as well.

I've been using 4.7 k resistors on the led, and I've used a mix of BS170's and 2n7000's for the mosfets and 2n3904s for the regular npns.

Thanks for any info!

[jmwreck]

i was not expecting somebody would have encountered this problem too, im way to throw my board, but after reading this, im thankful, that you have done or fixed that problem, since, ive changed all the millenium 2 components at least 5 times, and still LED is on, bypassed or not.

i hope this too will work for me.

[R.G.]

... I've run into a problem with the LED staying on all the time whether or not the effect is bypassed or engaged. I've fixed this problem on both by adding a 100K to 1M resistor from the board effect output to ground. ...
Is there a better way to avoid this issue in the future?

The Millenium Bypass is a resistance detector. It tells you whether the resistance to ground at the input is more or less than enough to "ground" the current leaking through the pullup diodes. For the specified diodes, this is normally about 1M. However, think about what happens if you use diodes that leak MORE than they should. This gives more current, so it takes a lower resistance to pull it down. If you have diodes that leak too little, the LED may never come on.

My guess is that your pullup diodes on the MIllenium are leakier than expected. Try changing them out.

I'm wondering if changing the current limiting resistor coming off Millenium 2 LED will fix the problem a bit more elegantly? I noticed on R.G. Keen's graphic of the Millenium 2 (http://www.geofex.com/Article_Folders/Millenium/milckt.gif) that he specifies a range of values for the current limiting resistor from 1K to 4.7K, hence my question. I'm not sure if the range was just to accomodate varying tastes in the brightness of an LED or if it has another function as well.

The LED limiting resistor has no other function. All it does is limit the LED current. It has no effect whatsoever on the switching threshold.