You have drawn correctly.
Yes it does matter.

NPN transistor vs. N-Channel mosfet (simplification).

Collector=Drain
Base=Gate
Emitter=Source

I believe Kermit2 has accidentally drawn the arrow on
the transistor (NPN 2n2222) pointing the wrong direction.
This may be confusing you.

that makes sense now. Because the base/gate are opposite parts, that would flip-flop the order.

 

Here's what I've come up with. Tell me how far off base I am, again. Monostable mode.

 

Okay, I've fixed the pic. NPN But regardless, this has progressed faster than I have. And yes the idea was to have you set the timing on one 555 with adjustments and have the other end/half do the relay driving.

 

Hello,

@Kermit2,
Also a current limitting resistor between pin 3 of the 555 and the base of the transistor is a must.
Other wise the 555 will try to push 200 mA into the base (for a standard 555).

Bertus

 

Hello,

@Kermit2,
Also a current limitting resistor between pin 3 of the 555 and the base of the transistor is a must.
Other wise the 555 will try to push 200 mA into the base (for a standard 555).

Bertus

just in time on that one. I just put the MOSFET in. All I have left are 3.3Kohm, will those suffice?

 

Hello,

For a mosfet a 100 - 220 Ohms resistor will be fine.
You are charging a capacitor on the gate with it.

Bertus

 

Okay, I've fixed the pic. NPN But regardless, this has progressed faster than I have. And yes the idea was to have you set the timing on one 555 with adjustments and have the other end/half do the relay driving.

that would be dandy- but then I'd have to add more control circuitry for the second half, no? IE trigger circuit and the power reset resistor?

So I could leave the first 556 in monostable (what I'm working on now), and we would use it to flip-flop the second 556? As in, I'm not wasting my time?

 

Hello,

For a mosfet a 100 - 220 Ohms resistor will be fine.
You are charging a capacitor on the gate with it.

Bertus

so I can use my spare 220 ohm (2 watt) resistor? Or should I use the 620 ohm?

I dont understand your second line

 

Build the circuit as you have it drawn, with the addition
of the resistor (220) that you have between the output
of the 555 and gate of the MOSFET. Then begin testing.

I dont understand your second line

He is giving insight into the INTERNAL workings of the MOSFET.

 

Build the circuit as you have it drawn, with the addition
of the resistor (220) that you have between the output
of the 555 and gate of the MOSFET. Then begin testing.



He is giving insight into the INTERNAL workings of the MOSFET.

thank you!

Should I use 220 or 620 ohm resisor? I have plenty more of 3.3Kohm, but that would be too high, no?

 

Here is where I am at right now.

 

Hello,

Like I said before a resistor of 100 - 220 Ohms between the pin 3 of the 555 and the gate of the mosfet.
If you go higher with the resistor value the turn-on time will rise and create more heat in the mosfet.
(it is the RC time of the gate resistor and the gate to source capacity).

Bertus

 

Hello,

Like I said before a resistor of 100 - 220 Ohms between the pin 3 of the 555 and the gate of the mosfet.
If you go higher with the resistor value the turn-on time will rise and create more heat in the mosfet.
(it is the RC time of the gate resistor and the gate to source capacity).

Bertus

ah, okay. 220 it is.

Thank You!

 

IT WORKS!

well, sorta.

since I don't have the .1uf cap for the edge-trigger nor the diodes to run the relay, i just set it up in a temporary basic mode- shorting trigger to ground, with an LED between source and constant in.

if I instantaneously short trigger to ground, the LED fires. If i hold it there, the LED turns off when i pul it away.

Looking at this image, I'm guessing that's correct, so far? it starts when first contact is made, so if trigger is held low for longer than output/capacitor, it will keep it lit until trigger goes back to 12 volts, correct?

resistor1 is rated 22ohm, actual: 219
resistor2 is rated 620ohm, actual: 615
pot1: range 0 to 490 ohm
pot2: range 0 to 490 ohm

capacitors are rated 1000uF (lets assume they're "fairly" close)
channel1 range: 219 to 709 ohm
channel2 range: 615 to 1105 ohm

channel1 RC range: 0.219 to 0.709 seconds
channel2 RC range: 0.615 to 1.105 seconds

actual time (using 1.1 rule)
channel 1: 0.20 to 0.65 seconds
channel 2: 0.56 to 1.00 seconds

So I missed the ball on channel 2 (both, really) I was aiming to have 0.5 seconds and 1.0 seconds be on the centers of the pot's adjustment. So I guess I get to just leave the pots wide open, unless we get good track conditions, then i can bottom them out and just do the minimums.

http://www.youtube.com/watch?v=ddhOvhNDOzQ

 

Hello,

Do you have a diode accross the relays coil, like in the schematic of kermit2?
Without the diode the mosfet will have a short lifetime due to the back EMF from the coil.

Bertus

 

For testing purposes when you cannot
get components look in any electronic "junk"
you have laying around. This stuff is usually a
"goldmine" for resistors and capacitors of
different values. Even the smallest items will
have a few caps and resistors. If you have something
laying around you may be able to find a small value
cap to test the edge trigger portion of the circuit.

 

Hello,

Do you have a diode accross the relays coil, like in the schematic of kermit2?
Without the diode the mosfet will have a short lifetime due to the back EMF from the coil.

Bertus

i dont have the relays connected. I just used an LED.

*looks through drawers, grabs an old PCI dial-up modem*

Found a 0.1 uF cap, now to de-solder it without killing it.

 

on the edgetrigger circuit, which way is the capacitor to be? negative to timer, or positive to timer?

 

updated the pic in case it can help anyone else reading this.

The cap for that portion of the circuit shouldn't be a polarized electrolytic type. It will probably work ok, but a non polarized cap(the disc shaped ones are one version) would be preferred.

You can make two aluminum electrolytics into a non polarized one by connecting the two negative legs to each other and using its positive legs in the circuit. By adding the diode around R3 in my drawing the large opposite polarity voltage spikes are snuffed out(snubbed). So with a diode in circuit an electrolytic cap will probably have a reasonably long live.

 

Kermit2,

I don't mean to hijack (although this is still pertinent),

By adding the diode around R3 in my drawing the large opposite polarity voltage spikes are snuffed out(snubbed). So with a diode in circuit an electrolytic cap will probably have a reasonably long live.

I thank you for the tip on the "snubber". I have seen this spike
in simulation and didn't know what to do about it. Now I do.
I did have concerns because the spike was as high as 24V when I
simulated it in LT Spice.

To magnethead,
Add the diode on your edge trigger portion of the circuit as a measure
of safety before cycling that thing too many times that spike could
be a problem for the chip when repeatedly cycled.