Article: Dew Heater Control and the Arduino

[rcheshire (Rowland)]

Not sure if this is helpful? if you are using, data types unsigned int; or unsigned long; they don't store negative numbers... int; and long; do.

-32! Ouch. I remember -20C with a wind chill of -35 in Goose Bay one time. Best to stay indoors.

[DancesWithWords]

Originally Posted by rcheshire

Not sure if this is helpful? if you are using, data types unsigned int; or unsigned long; they don't store negative numbers... int; and long; do.

-32! Ouch. I remember -20C with a wind chill of -35 in Goose Bay one time. Best to stay indoors.

Looking at the code it looks like Sungjune used 32bit unsigned type.

// note that all the time variable should be 32bit unsigned.
static uint32_t system_tick = 0; // ever increasing from zero
static uint32_t slcd_timer = 0; // timeout count for the LCD backlight
static uint32_t encsw_timer = 0; // timeout count for the encoder switch

// this value is used to determine the heater control
#define DEWPOINT_MARGIN 500 // 5 degree in celsius

static int16_t dew_point = -1000; // initial value(-10 degree)
static int16_t ambient_temp = 0; // ambient temp. in Celcius (x100)
static int16_t ambient_humid = 0; // relative humidity in percentage
static int16_t mirror_temp = 0; // mirror temp. in Celcius (x100)

===
DWW

[rcheshire (Rowland)]

uint data type seems to apply to timing for various functions. If timing is exceeding the storage value I think it will loop around to negative values. In that case, I think long unsigned int will provide significantly more margin for your timer/timing.

I'm no expert, but you could try long uint instead. No need for temp calculations as they require +/- values provided by int.

[Bassnut (Fred)]

Originally Posted by hikerbob

BTW, I've ordered some bit's to try a Veroboard version of the remote controller. Not sure how much effort would be involved in getting the existing controller to talk to it but given I'm already using I2C maybe not too bad.

If it works as expected I'd have to look at some options for a surface mount version.

Since I wrote that I've been having another look at the pinout's for the 8M2 and am not sure that I can do both PWM and I2C, the one pin labelled with pwm is also the I2C SDA pin.

Should be able to do a version of PWM in code on another pin. Failing that look into the 14M2 chip's which do have PWM on pins seperate to I2C.

Bob

I use Picaxe i2c all the time, it's a snitch. Why the hang up with PMW?, why do you bother with it at all?, a very simple timer function or even just a padded for-next loop is all that's required for a dew heater . Any thing faster than a 1 sec period is a waste of effort and just creates noise. An 8m2 will easily do the job with i2c.

[alistairsam]

Hi,
I'd agree with Fred. I don't think pwm is necessary at all. I've got a 4 channel working fine based on freds code in post 48 using one 20m2.
for pwm and i2c, have a look at the x2 series, 20x2 or 28x2.
they have a lot of features and I have 3 x 20x2's at 64Mhz talking on I2C and pwm as well the hardware timer in the background.
I think 20m2's do that as well.
Are you making a remote controller? I couldn't find your post on the remote control Bob.

[rcheshire (Rowland)]

If that's what you have on hand pwm is suitable and easy enough to do.

I bung a 22uf cap across the FET gate and GND which generates a slightly rounded at the peaks sawtooth wave +/- 0.05v. Is that smooth enough?

[Bassnut (Fred)]

Originally Posted by rcheshire

If that's what you have on hand pwm is suitable and easy enough to do.

I bung a 22uf cap across the FET gate and GND which generates a slightly rounded at the peaks sawtooth wave +/- 0.05v. Is that smooth enough?

PWM is harder to do and just plain inappropriate for a dew heater application. Sledge hammering the out put with a cap is energy sapping and heat generating (in the wrong place), daft

[rcheshire (Rowland)]

PWM is harder to do and just plain inappropriate for a dew heater application. Sledge hammering the out put with a cap is energy sapping and heat generating (in the wrong place), daft

Oh dear! I guess that's the burning smell and smoke I see from time-to-time. Perhaps I don't need the capacitor after all? I guess it's a bit more convenient than holding a cigarette lighter under the lens. That got a bit tedious after a while.

Cheers Fred. Don't mention PWM - specifically with reference to dew heaters - got it! Totally inappropriate - silly, in-fact