Adafruit PCA9685 PWM Servo driver with SparkFun ESP8266 Thin

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adafruit_support_mike
 
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Re: Adafruit PCA9685 PWM Servo driver with SparkFun ESP8266

Post by adafruit_support_mike »

I've tested the IRLB8721's channel resistance with the gate voltage near 3V, and it does work.. I was concerned about that myself.

The point where the channel resistance drops below 1 ohm seems to be near 2.9V. That's still unacceptably high for current loads of several amps, but with 3.3V of gate voltage I was able to send 3A through one and measure less than 500mV between the drain and the source (the practical way to measure channel resistance).

How much current are you sending through the mosfets?

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zhulien
 
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Re: Adafruit PCA9685 PWM Servo driver with SparkFun ESP8266

Post by zhulien »

Like I said, I'm driving 12V 60LED LED strips of varying length. Basically, they're between 2 and 5 meters. At max intensity(brightness) the current per meter should be around 1.2A, so 6A at most(for 5m) for a RGB LED strips. I tested with a UV 60 LED strip, but the current should be the same(1.2A per meter - 6A at most for 5m at full brightness). The difference is RGB are 3 channel and UV are 1 channel. So in the case of RGB I drive each channel through a separate MOSFET which should basically cut the Amperage to 1/3 per meter I suppose so it should be 0.4A/m, 2A/5m at max intensity. I'll try once again the whole setup through the Arduino and then swap the UV for a RGB channel to decrease the current and try again with the ESP8266.

This is for constant max brightness, though. Considering I'm trying to PWM the strips based on audio input, the load should be less than half I suppose.

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adafruit_support_mike
 
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Re: Adafruit PCA9685 PWM Servo driver with SparkFun ESP8266

Post by adafruit_support_mike »

6A is enough that you'll need very low channel resistance to avoid excessive voltage across the mosfet.

The best way to find out what's happening will be to connect the load to the mosfet through an ammeter, and get simultaneous measurements of currnent through the mosfet and voltage between the drain and source when the gate is being driven by the ESP8266. Those values will let you estimate the channel resistance.

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zhulien
 
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Re: Adafruit PCA9685 PWM Servo driver with SparkFun ESP8266

Post by zhulien »

Just to post an update. I tried again with the Arduino, everything works fine. The ESP8266 can't even lit the strip(at all). 6A is the most extreme case. Most of the strips are 3m and are split by color channel so 3 MOSFETS per strip which will equal (3m*1.2A(for absolute full brightness))/3 = 1.2A per MOSFET and once again this is the most extreme case in which we drive a constant full brightness through the strip. PWM-ing should decrease this to at least half as average.

I start to think I am not connecting the ESP8266 properly to the Servo driver or I need to do code alterations specificly for the ESP to work with the library. I'll test the connection by driving a single LED by the ESP-PWM driver and if this goes well, the problem should be in the transistors so I'll maybe either buy new ones or search for another solution for the microcontrollers.

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