dimming LED strips

MrDEB · Mar 20, 2023

ran across this schematic and thinking of incorporating into my next sign PCB.
QUESTION maybe a 1K resistor before the gate to protect the gate?
Planning on using a smd pot

Kerim · Mar 20, 2023

What did you choose as Vcc?
Which LED strip you chose?

MrDEB · Mar 20, 2023

12 volts input. Various lengths of LED strips different colors as well

Nigel Goodwin · Mar 20, 2023

MrDEB said:
ran across this schematic and thinking of incorporating into my next sign PCB.
QUESTION maybe a 1K resistor before the gate to protect the gate?
Planning on using a smd pot

It's pretty well the poorest circuit you could find - you could only make it worse by losing the FET and using a low value pot.

MrDEB · Mar 21, 2023

after some research, the most the mosfet will have to handle is approx 5 watts.
The pot will be hard wired to the PCB. The company selling the LED/neon rope lights has a dimmer that can be used. Will consider

Nigel Goodwin · Mar 21, 2023

MrDEB said:
after some research, the most the mosfet will have to handle is approx 5 watts.
The pot will be hard wired to the PCB. The company selling the LED/neon rope lights has a dimmer that can be used. Will consider

Use their dimmer, presumably it costs hardly anything? - it will be a 'proper' one, not like the crap one from circuits-diy

And 5W is a LOT of heat, and would require a large heatsink

Tony Stewart · Mar 21, 2023

You can use a PWM circuit to drive a power FET high (P)ch) or low side (Nch) such as a LM555 PWM with a pot. Then it will be efficient. Choose f = 1k to 5 kHz or buy a proper remote control controller with LEDs is best.

MrDEB · Mar 21, 2023

they want $39 for a dimmer

Tony Stewart · Mar 21, 2023

You need to do better shopping. https://www.temu.com/ca/1pc-100ft-l...istmas-home-decoration-g-601099513176918.html.

Nigel Goodwin · Mar 22, 2023

MrDEB said:
they want $39 for a dimmer

Then consult google - they are available for less than £2 - even remote control ones are stupidly cheap.

MrDEB · Mar 22, 2023

It dawned on me that the 18f2221 chip I am going to use has several PWM pins.
Now to experiment with PWM.

MrDEB · Mar 22, 2023

After researching the data sheet I see the 18F2221 has 5 PWM outputs.
Now to test the Swordfish code and see if it is what I can use.

Nigel Goodwin · Mar 22, 2023

MrDEB said:
It dawned on me that the 18f2221 chip I am going to use has several PWM pins.
Now to experiment with PWM.

It's considerably cheaper to buy one ready made for less than £2 - but it's trivial to make a PIC based one.

tumbleweed · Mar 22, 2023

MrDEB said:
After researching the data sheet I see the 18F2221 has 5 PWM outputs.

FWIW, the 28-pin 18F2221 has two CCP/PWM peripherals... CCP1 and CCP2.
CCP1 output is on pin RC2, and CCP2 output can be either RC1 or RB3 depending on the CONFIG CCP2MX setting.

MrDEB · Mar 22, 2023

the data sheet I read has Portb.0 = pwm
ports c.1, c.2 are pwm
portd.6 & 7 = pwm but maybe other than the 28 pin package.

tumbleweed · Mar 22, 2023

PORTB.O is the fault input for CCP1, not the pwm output

Obviously there's no PORTD on a 28-pin part

For The Popcorn · Mar 22, 2023

Is it Ground Hog day again?

Nigel Goodwin · Mar 22, 2023

For The Popcorn said:
Is it Ground Hog day again?

Yep

While here is exactly what he needs for £0.92

https://www.aliexpress.com/item/1005004291620707.html?spm=a2g0o.productlist.main.19.588350be9ApEI1&algo_pvid=429d7d94-e637-4ef3-b5ab-c808deaebb28&aem_p4p_detail=202303220920082560380048785290006023777&algo_exp_id=429d7d94-e637-4ef3-b5ab-c808deaebb28-9&pdp_ext_f=%7B%22sku_id%22%3A%2212000028650909979%22%7D&pdp_npi=3%40dis%21GBP%211.44%210.92%21%21%21%21%21%402122457116795020081261988d0713%2112000028650909979%21sea%21UK%211751606289&curPageLogUid=HHpH8x72JjOP&ad_pvid=202303220920082560380048785290006023777_2&ad_pvid=202303220920082560380048785290006023777_2

For The Popcorn · Mar 22, 2023

For The Popcorn said:
Is it Ground Hog day again?

Again and again and again and again.......

MrDEB · Mar 22, 2023

am I reading these data sheets correctly?
portb.3, c.1, c2, are all PWM outputs?

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