Other Parts Discussed in Thread: LP5569
am trying to follow this example
Programming Example:
Dim LEDs 0 to 7 at 1 Hz at 25% duty cycle
1. Set PSC0 to achieve DIM0 of 1s
2. Set PWM0 duty cycle to 25%
3. Set PSC1 to achieve DIM1 of 0.2s
4. Set LEDs 0 to 7 to point to DIM0
In the spec sheet.
Below this programming example is a table with the values of the registers. Running my code I get
Duty cycle 0x3f PWM0
Period 0x9f PSC0
Period 0x1f PSC1
Duty cycle 0x3f PWM1
Period 0x9f PSC0
Period 0x1f PSC1
Duty cycle 0x3f PWM1
which agrees with the expected values given in the table.
I do not set all the LEDs but only LED1. However, all this LED does is blink. There is no dimming. Also, it is not clear what the role of DIM1 is even though I set it.
Is the example wrong? Is there missing information given that DIM1 is set in the example but it is not used.
Otherwise I can set two independent blink rates for each of the LEDs. That works. But I cannot get any LED to DIM. Please help and complete what is missing in the example.
I can make the LEDs dim by continuously changing the duty cycle in a for-loop every couple hundredths of a second. But that defeats the reason for having the LP3944 as it obviously puts a big load on the I2C bus and the processor.
Please point me to more examples
Here is my python code (on Raspberry PI) to set DIM0 and DIM1 via the prescaler and pwm registers:
def lp3944_dim_set_period(self, dim0_or_dim1: boolean, period: int) ->int:
psc_reg = LP3944_REG_PSC0 if dim0_or_dim1 else LP3944_REG_PSC1
# Convert period to Prescaler value */
if (period > LP3944_PERIOD_MAX):
return -1
psc_value = (period * 255) // LP3944_PERIOD_MAX
psc_dim = "PSC0" if dim0_or_dim1 else "PSC1"
print("Period " + str(hex(psc_value)) + " " + psc_dim)
err = self.lp3944_reg_write(psc_reg, psc_value)
return err;
def lp3944_dim_set_dutycycle(self, dim0_or_dim1: boolean, duty_cycle: int) ->int:
pwm_reg = LP3944_REG_PWM0 if dim0_or_dim1 else LP3944_REG_PWM1
# Convert duty cycle to PWM value */
if (duty_cycle > LP3944_DUTY_CYCLE_MAX):
return -1
pwm_value = (duty_cycle * 255) // LP3944_DUTY_CYCLE_MAX
pwm_dim = "PWM0" if dim0_or_dim1 else "PWM1"
print("Duty cycle " + str(hex(pwm_value)) + " " + pwm_dim)
return self.lp3944_reg_write(pwm_reg, pwm_value)Its the pre-scaler register that is not behaving as I expect. I can do a simple loop and continuously set the pwm register and make it dim/brighten in that manner. So the pwm register IS behaving as I expect.
