is my circuit practically complete?

[panjangsangat]

using proteus, ISIS 7 Professional I have simulate that circuit and it seems working but is it practical if i build the circuit just like in the proteus? have i put transistor, diode or other component to make the circuit more practical?

tq..

 

[BrownOut]

For one thing, you need a reversed biased diode across the relay coil to snuff out inductive spikes that might otherwise destroy the IC.

 

[Dick Cappels]

I would think that the active pull-down device will handle the "flyback" current.

You might want to connect the wier on the VR so that the VR adjusts the timing.

 

[panjangsangat]

I would think that the active pull-down device will handle the "flyback" current.

You might want to connect the wier on the VR so that the VR adjusts the timing.

actually, i dont really understand about "the active pull-down device will handle the "flyback" current" thing. can u explain it to me?

tq

 

[Nigel Goodwin]

I would think that the active pull-down device will handle the "flyback" current.

No, you need a diode across the relay.

 

[Hero999]

That are the relays driving?

I've never seen that symbol before, did you just make it up?

 

[Mikebits]

Looks like maybe they are piezo buzzers?

How much current does your relay require?

 

[panjangsangat]

Looks like maybe they are piezo buzzers?

How much current does your relay require?

it doesnt state the relay current and i dont use any piezo buzzers there...

and about relay driving.. are u mention about RV1? it is potentiometer.. i take from library..

 

[Mikebits]

So what are those little black circles then? You need to know the current draw of your relay. What is the part number on it?

 

[panjangsangat]

that black circles is 12v dc motor..

about the relay, it part number is RTD24012F..

actually, do the current draw of the relay will effect the circuit?

 

[Hero999]

The relay probably uses more current than the piezo buzzers.

Why not connect the piezo buzzers directly to the output of the 555?

If you want a two tone you could just use a NE556 and a piezo transducer (with no internal oscillator) or a speaker.

 

[Hero999]

that black circles is 12v dc motor..

Forget my previous idea, unless the motors are really tiny.

This forum software is really annoying me.

 

[panjangsangat]

nvm, so do you have any suggestion about my circuit?

 

[Mikebits]

I can't find a data sheet for the relay part number you gave. The 555 has a output current spec and this needs to be met. Your relay draws some amount of current which your 555 needs to supply and you must know this number. Without a data sheet you are only guessing and this is a bad practice to get into. I suggest you obtain the relay data sheet or pick another relay where you can obtain the data sheet.

 

[Hero999]

How much current do the motors use?

Why not use transistors to control the motors?

 

[mneary]

I would think that the active pull-down device will handle the "flyback" current.

You might want to connect the wier on the VR so that the VR adjusts the timing.

Unfortunately the current needs to flow in the wrong direction. It's OK with NMOS where the channel is ON in both directions but in bipolar devices the reverse mode beta is very low. The flyback current would end up in the esd diodes.

[edit] See correction by Dick Cappels in next message.

 

[Dick Cappels]

actually, i dont really understand about "the active pull-down device will handle the "flyback" current" thing. can u explain it to me?

tq

In the 555 (regardless of type, CMOS or bipolar) there is a transistor on the output to pull pin 3 high and there is another one to pull pin 3 low.

When pin 3 goes high, it causes current to flow into the relay coil, that current is limited by the coil's resistance and the output voltage of the 555 according to Ohm's Law.

When pin 3 goes low, the magnetic field around the relay coil will collapse, causing current to keep flowing through the coil, and to do this the coil will drive pin 3 toward ground.

If the 555 is an NE555 (with bipolar transistors), the transistor that supplied the current to the realy's coil is an NPN Darlington, the emitter of which is connected to pin 3.

When pin 3 switches low, the emitter of that NPN Darlington will continue to supply current to the realy coil as the magnetic field collapses, thus holding pin 3 near ground.

If the 555 is a CMOS version, then things are as above, except when pin 3 switches to ground, the parasitic diode that is part of the MOSFET that pulls pin 3 low will conduct the current from the relay coil as its magnetic field collapses, thus holding the voltage on pin 3 to a little below ground until the filed has collapsed.

Sorry, but I mistyped "Wiper" in my earlier reply. The wiper of the VR needs to be connected to one end of the VR or the other.

 

[Hero999]

A diode is required because the transistors have a finite switching time.

I'm also not connived there's a parasitic diode on a MOSFET internal to an IC in the same way there is in a discrete MOSFET?

Here's how I'd do it anyway, I don't see the need for a relay, a couple of transistors is much cheaper.

EDIT:
Please turn the grid off before posting schematics in future.

I've also corrected it to use the proper motor symbol but I suspect that the non-standard symbol used by your CAD package isn't your fault.

 

[panjangsangat]

thank you for your suggestion about transistor.. can you provide me the transistor product number and what kind of transistor you use..? I want to study its function and how it works on internet.. really apreciate this..

 

[Hero999]

It depends on how much current the motor uses?

For up to 1A use BC635 (NPN) and BC636 (PNP).

The 220R resistors both need to be rated to 1W.