Electronics FAO Cpemma (Or other such Electronics Luminary) - RE Diode Bus

My transistor theory is a bit shaky, but it seems from simulations that if the collector current is fixed by the load, base current should be limited to load current/gain.

That's ideal world, any short on the output would pull a high base current, which a base resistor would limit. So I think they're a safety device.

 

Guys - I'm confused! (Not difficult, I know...)

The Blue LEDs I was thinking of using have a voltage forward of 5.5v.

I read in another post that to get the value of the current limiting resistor, I add up the voltage forward values - So off a 12v supply, I'd only be able to run 2 in series, according to the Linear's calculator.

So how do I get 6 to light up bargraph style?

 

That is a pretty high voltage for an LED.
(They may be a first generation Blue LED)
If they are indead that high, yes you can only run two in series.
To get six you will have to wire two sets of three in paralell.
Each set will need it's own resistor.
And the transistor should be able to handle the extra current without any problems.
If you are worried, or want to run more than one fan off this, you can use power transistors.

 

Wouldn't that mean that it'd be all off, 3 on or 6 on? The effect I'm after is a one by one increase in the number of LED's lit.

Can it be done?

 

Opps,
/me looking at schematic again...

Oh, the LED's light in sequence, so it goes in series through each LED lighting them in turn....

You have two choices.

Seperate each LED as runs a resistor for each, this will provide a one LED indicator, showing the current level.

OR

Get different LED's

 

OK - so next question is does anybody know where I can get blue led's that have VF < 2v ?

 

My diobus circuit takes care of that problem. With those leds you'll need to use 3 lots of 2 in series, with the steering diode arrangement keeping the lower voltage strings on when the switch is in the higher voltage positions.

So from switch pins 9 and over, a diode and resistor also goes to the pin 8 led to keep the first string on, as well as to the second or third strings. From pins 11 & 12, two steering diodes will be needed, to the first & second string of leds. Gets a bit cluttered, but is possible

You'll notice even with 2v reds, you need at least 2 strings.

 

Great - I'll have thunk and draw up a new schematic.

Thanks to both of you (Zap & CP)

GOO

 

Right - Here's the latest attempt. This splits the six leds into 3 groups of 2, and the limiting resistors have been calculated using a VF of 5v and IF of 30mA. I've put in Schottky diodes like in Cpemma's switch diodebus to control the flow to the LED's.

Diode-Bus II Take Two

Look Ok?

Ta,

GOO

 

The motor control side looks OK (I'd use 2 diodes at D14), but you've got the display signal coming from the various transistor emitters, which are also grounded, so that's a

That said, I can't see where you can connect the display sources suitable for a bargraph with your circuit as it stands. The complex way would be to pair up all the transistors, one in the motor circuit and one in a display circuit, but there may be a simpler method (other than a 3914 across the fan).

 

Here's one that may work (caveat actor), added on to the 4017 knight-rider circuit.



However, a major snag (IMO) is that the circuit doesn't "remember" fan settings when you turn the box off.

A more minor snag is that any fan speed signal shouldn't be used, as fan negative is above ground potential.

Anyone for PICs?

 

Fan speed sensing isn't really a big issue for me, as I don't get it on the intakes of my Lili now. Plus I know how fast there going by a) the sound and b) the LED's.

Cheers for the circuit though! Need a trip to Maplins for supplies!

 

Just to stirr an old topic, has anyone been able to make a pushbutton fanbus that does remember the state it was previously?

If so, then I would like to know how it can be done. At first I was thinking about ripping some juice from +5VSB line, but thought that it should somehow remember state anyhow

 

It might be worth looking at NiHiLiST's One Button, One Dial, One Baybus, WAY too many ICs project as it is tackling some of the same problems.

 

yes I have read that couple of times but it does not answer that question, how to remember old state after shutdown. It does have couple of truly nice features though...

 

Could you not use something like this.

 

Nice one, Orb, You just pointed me to one of my own postings

The reason I would like to do it 4017 style is that it would be so easy to get leds to display the fanspeed. If this is not possible, then Ill just have to do it with that DS1809 I mentioned in that other posting and attach a LM3914 to it to get bargraph

Marvin, please start a new thread rather than re-open one that's as old (and not all that relavent) as this one, & oblige cpemma..