555 Timer Question

Yes, you're right! I didn't look at the circuit carefully. It's just like measuring a battery with R probe to + and B probe to - and the next moment reversing the battery with R probe to - and B probe to + so the meter reads +9 and -9 resply.

I've seen this type of connection in a wired intercom system where the amplifier and master speaker is on one side while the other end is just a slave speaker. The change over switch makes the master spk behaves as a mic and the slave spk as a receiver. If the switch is pressed the slave becomes a mic while the master becomes a receiver.

Thanks for correcting my mistake.

Allen

Hey Allen,

I'm getting the -9v from the relay switching the neg and pos around.. IE.. like changing polarities on a battery. Soo.. the positive period would have

+9v and the negative period would have a -9v ... there wouldn't be a 0 (zero) voltage time... That chart shows the voltage output during a 30 minute period...

Dave

Can this circuit

use a mini or sub-mini latching bistable reed relay? If so, I would prefer it, as it needs to be a battery-run device.

Not as it's shown, no. You need to either drive two coils, or hit the coil with an opposite polarity, depending on the typs of relay, so you'd add a little complexity, to get the reduced power consumption.

Good Luck! Rich

One final question: If the coil on the relay is something other than

400 ohms resistance, how does that change the values of other comp> Here is the schematic...

If the relay resistance goes below about 50 ohms, you'll need a smaller resistor between the 555 and the NPN's base. The problem is that if the relay wants too much current, and the base current isn't large enough to pull up Vbe and saturate the transistor, the relay may not close.

What are you timing?

--
Regards,
  Bob Monsen

"I am turned into a sort of machine for observing facts and grinding
out conclusions."
 -- Charles Darwin

it could be modified to do so, (keep the 4060 and timing components, throw the rest away)

you'd need to arrange for the relay to get opposite pulses to turn it on or off.

the details of that depend on the relay you want to use... for one with separate coils to switch each direction something like this could do it +9 | +-------+ ||+ | | +---||-[2k2]---------)-------)-----. | || | | | | 10uF | +--|