led flasher

http://m./itm/151110546574?cmd=VIDESC&gxo=true

For whatever reason i cant post eeeebayyyt link so i copied and pasted below.. Specification:1. use as a square-wave signal generator, generate square wave signals used for experimental development.2. to generate square wave signal driving stepping motor drive.3. adjustable pulses generated for use by the MCU.4. adjustable pulse control related circuits.Description:size: 3.5CM*3.6CM1, Main chip: NE555;2, Input voltage: 5V-15VDC. (When 5V power supply, output current =15MA; when 12V power supply, output current=35MA);3, Input current: ≥ 100MA4, the output amplitude: 4.2V V-PP to 11.4V V-PP. (according to the different input voltage, output will be different)5, Maximum output current: ≥ 15MA (5V power supply, when V-PP is greater than 50%), ≥ 35MA (12V power supply, when V-PP is greater than 50%)Characteristics and advantages:1, output with LED indication(low level LED ON, high level LED OFF, at lower frequencies than the LED flashing);2, the output frequency range level can be selected, the output frequency adjustable;Low frequency: 1Hz~50HzMF: 50Hz~1kHzHF: 1KHz~10kHzHF: 10kHz~200kHz3, the output duty cycle can Adjustable(Small), adjustable duty ratio will change the frequency.4, the output frequency adjustable;Cycle T=0.7 (RA+2RB) cRA, RB for the 0-10K adjustable;C=0.001UF low frequency gear;C=0.1UF MF gear;High frequency in document C=1UF;C=100UF high frequency gear, wave frequency buyers can own calculation.

What? Haven't you read the sire rules? (Oi - reading and forgetting is cool!!) eBay links are not accepted, but all you need supply is the item number so I now have the US $3.49 NE555 pulse frequency adjustable module Square/square wave signal generator. That has two big caps and I'd assume one is for power smoothing since it uses 3 selectable caps depending on frequency range (big, medium & small). I note it specifies a mere 15mA or 35mA output etc - so what about the 555's normal 200mA output (at 12V)? (ok, maybe 20mA of that goes to the LED.) But the spec is unclear - why say output is "≥ 35mA (12V power supply)" when it should give a max output capability (eg, 150mA or ≤ 150mA)? Inability to supply the load could cause problems. Normally it'd blow the 555 (if above the 555 spec) but since this is a lower output spec current, is its supply limited somehow, or output buffered? I need to see the module's circuit... OK TinEye or google images... PS - I had no luck finding its circuit.

151110546574 is the item #. Ill snap a photo of it?

Also... given the 3$ price if need be i can grab a different fasher if needed.

Nah - I got the eBay link - ie, after "itm" in the site-censored link is the item number so I could go to eBay & search. Hence why I gave the eBay "title" above. It's pic is: And now I see your diagram on page 1 (I didn't see that before). But that is different to what I described. But I note that the RainLight spec claims 250mA which is too much for a 555, and maybe too much for that 555 module (if it's 35mA etc). Note that the RainLight claims 130mA @ 13.5V = 1.8W (flashing) but that will be an average figure and it is still a 250mA load (ie, 130mA/250mA suggests a 50% on-off flashing duty cycle). Finally I presume you have the CK-LR-15 non-flashing RainLight as the others have their own smarts and you cannot flash those (using an external circuit). Mind you, yet again I see ambiguities...

The Cartek Dual-Colour Dual-Function Rain Light sheet says:

Black - Earth

Red - RED RAIN LIGHT (static)

Yellow - AMBER FLASHING

... but doesn't say how to connect.   

I'd assume black is earth/GND (cool) and you connect either Red or Yellow to +12V for static Red or flashing Amber respectively.    

But the cartek FiARAINLIGHT page has the Simple 3 wire connection to LED rain light animation which only shows ONE wire to the Rain Light.   

I can only assume that that Electronic Rain Light Switch has its own internal flasher etc and is thus used on any Rain Light provided it is NOT any flashing RainLight like the CK-LR-F3 or CK-LR-DC.   

Not that their switch has any specs (like max load), but why do suppliers or manufacturers make these things so difficult to understand?   Or is it just me? Wow - £89.00 for the plain static CK-LR-15. I wonder how that would compare to a DIY unit using 60 per meter SMD LEDs? eg, eBay item 35cf2332e1 ($10 for 5m = 4c per LED for the "big" 5050 SMD LEDS). But note that those "12V" are 12V regulated, NOT 12V automotive - they need an external resistor for typical up to 14.4V automobile use. (Ideally one resistor per string of 3 LEDs, else voltage limited using a resistor & Zenor diode circuit, or why not ensure constant brightness irrespective of voltage by using a dc-dc converter?) Anyhow, you 555 module will not handle the CK-LR-15 or others since the 555 is 200mA limited and there is no buffering (amplifying) transistor on that module. You need to add a transistor or MOSFET to handle the 250mA, and that should be on the +12V side to simplify the circuit. PS - the strikethru is intentional. I figured I'd leave my iterative ramble, and criticism.

Damn your the wizard... :-) my cartek is the static model only two leads + and ground. Given my novice, how would the mosfet apply in layman terms? Replacing the 555 or suplement? Gotta forgive me im learning as i go.

"only two leads + and ground." - meaning 2 leads plus a GND, or 2 leads - a plus & GND? If 2 + GND, what are the 2? One is obviously full on. The 'buffer' - eg, a (bi-polar) transistor, or a MOSFET - is an add-on. When things like 555 circuits can't supply enough power (usually current), we add a buffer (for want of a better term). Think of a relay. Though often used merely to switch (remotely) etc, it is often used so that small switches can supply huge currents. EG - a typical automotive relay can switch 30A but only requires maybe 60mA to 250mA to turn on. In some ways a relay is like an amplifier - small current in, big current out. So too is a transistor which typically has a maximum gain aka "Beta". EG - you may choose a 1A capable transistor to turn on your 250mA relay or LEDs. Let's say we decide to have it supply 500mA and it has a gain of 50. We supply 500mA/50 = 10mA to its "Base".

That's in simple terms. There are technicalities like the Base must be at least 0.7V above its Emitter (for a common NPN transistor), but otherwise the Base is a bit like a relay's coil and the transistor's Collector & Emitter are line the heavy relay contacts (aka 30 & 87).

That's using the transistor as a switch (sometimes known as digital mode) - ie, we either feed it 10mA or nothing. Your 555 circuit can supply 10mA hence we can turn the transistor from fully off to fully on and hence "switch" up to 500mA - enugh for your relay coil or LEDs.

If we vary the transistor's base current from say 0.1mA to 10mA then we vary the transistor's output from 5mA to 500mA. That's how amplifiers work.

But let's forget about that "analog" mode...

A MOSFET is a special type of transistor, but FETs use a voltage to vary output current.

"Transistors" usually refer specifically to "bipolar" transistors like I described above whereas FETs include FETs, J-FETs, MOSFETs etc.

MOSFETs are a type of FET that can handle big currents eg, 100A. And since a 50A - 100A capable MOSFET might only cost $2, we might use it anytime a FET is required.

I like MOSFETs because they are simple - at least in switching mode. With a Vgs above maybe 4V, the output is fully on.

Vgs is the FETs Gate to Source voltage which is equivalent to a (bipolar) transistor's Vbe - Base-Emitter voltage.

However the current required to turn on a FET is negligible - ie, usually nano-Amps. (IOW it has VERY high resistance - typically many Mega-Ohms - and it does not "load" the driving circuit.)   

And we don't worry about the "gain" of a FET, at least not in full-on & off switching mode. Besides, it's not a current gain, it's a voltage-current transfer function.

I should have referred you direct to wiki or even better electronic tutorials (maybe bcae1.com?), but maybe a bit of an intro helps.

Now I use MOSFETs to connect grounds, hence N-ch = N-channel MOSFETs which are equivalent to npn transistors - ie, Vg or Vb is +ve wrt to the Source or Emitter (Vgs or Vbe are +ve).

But to switch the +V side (ie, +12V) requires the mirror image P-ch type (equiv to a pnp transistor) where the Gate is more -ve than the Source.

P-type MOSFETs are less common and fewer are able to supply the high currents of N-ch FETs, but the few Amps you need are no problem.

Anyhow, whether a tranny or a FET, both are add-ons.

They'd probably both be added to the 555 board with Emitter or Source to +12V, and Collector or Drain to the load (LED, relay coil, etc).

Both would have a Base or Gate resistor to the 555 output, and a resistor from Base or Gate to +12V.

The transistor's base resistor is to limit its base current and in conjunction with the base-emitter resistor sets a Vbe voltage of ~0.7V. (IE - that design requires various calcs.)

The MOSFET usually doesn't need any such resistors BUT a b-e - I mean, gaste-source resistor is added to ensure the FET is off when no voltage is applied (remember it only takes nA to turn on - hence a finger, or moisture, or electromagnetic noise)...

And a base - I mean gate resistor is used to protect the driver (ie, 555) from damage in case of a certain FET failure mode (where big currents can flow thru the normally insulated nan-Amp gate).

Why do I like MOSFETs? It's those bluddy resistors.

EG....

I know 82 Ohms is the minimum resistance to limit a 555 output to 200mA at 12V. (Check: V=IR. Assume V = 15V; i = 200mA, hence R = V/i = 15/0.2 = 75 Ohm, hence 82 Ohms being the next preferred resistor value.)

The gate needs nA. Let's assume 1uA @ 5V. R = 5V/1uA = 5MR (Mega-Ohms) max to pass at least 1uA. (Note - 5V because we assume Vgs = 5V to fully turn on and lest assume a low system voltage of 10V, hence 10V les 5V - 5V).

So Rg (gate's series Resistor) can be 82 - 5M Ohms. That's a heck of a range of choices! But let's drop 5M to 1M for extra "ensure sufficient gate current" extra current.

What about the "ensure turn off" Rgs (gate-source resistor)?

Well, similar to above, a 5M or higher resistor should be more than enough, but let's make it 1M.

The ONLY consideration is that Rg & Rgs form a voltage divider between the driver (555) and Source, but just ensure Rgs is at least 10x larger than Rg and that becomes negligible (ie a 10:1 resistor ration means less than a 10% change to the input voltage.

So if Rgs = 1M, then Rg can be up to 100k but above 82 Ohms to protect the 555.

Hence Rg can be 100 Ohms or 1k or 100k or anywhere between.

In fact for a 555 circuit where its output is either GND or +V (eg, +12V), we don't need that Rgs, but let's say the 555 has failed or its output is floating (maybe a broken track) and we want to ensure the FET is off unless it is supposed to be on...

Oh dear, there's a lot there, but I actually cover a lot of design considerations.

In summary, a transistor requires "design". But a MOSFET can usually carry more current with less heat and is cheaper than a transistor, and really doesn't need any design. Just add an optional gate-source resistor to ensure turn off and an optional (series) gate resistor if you want to protect whatever is turning the MOSFET on or off.

Either can often be 10k to 1M in practice. Only the minimum resistance to protect the driver need be calculated. (Make it easy, eg for a 555 with 200mA assume a mere 100mA, and then 10V or 20V => 10/0.1 = 100 or 20V/0.1 = 200 Ohm.)

And make that 'input' (series aka Gate resistance) Rg at least 10x smaller than the Rgs turn off resistor (if that is used).   

After a while you just realise that an Rg or 1k or 10k can be used with an Rgs of 100k to 1M for most cases (ie, 12V & 24V systems).

That's why I consider MOSFETs so easy to use (or rather, design).

A final note (at last): A FET is simply described as a (gate) voltage that varies its output (Source-Drain) resistance.

(See you in a few weeks???)