I2c, srf02, 16f688 -> ultrasonic rangefinder

[RussMartin]

Peter, thanks for chiming in. I added the parentheses. Still nothing, but it's a good point nevertheless.

Yes, FAR is greater than NEAR. In fact, the way I have the pots configured, NEAR can never be greater than FAR.

I just checked again; during the 5-second "blinky" phase, the SRF02 is quiescent. It then responds by pinging on command (I can "see" the ping with an ultrasonic receiver and a scope--and it's appearing about once a second, as it should).

Al, is there an error in the 16F688 manual? I'm looking at Table 1-1 (page 6) and it shows A4 as TTL in, CMOS out. (In fact, I can't find an OC legend anywhere on the chart!)

I'm fairly convinced the problem is somewhere in how I'm manipulating the data, or perhaps I have misdefined something.

[Bruce]

You want to write directly to ADCON1 so you have at least Fosc/8 for 4MHz.

ADCIN doesn't do this for you - so your AD conversion clock is way too fast with ADCON1 = 0 by default.

[RussMartin]

You want to write directly to ADCON1 so you have at least Fosc/8 for 4MHz.

ADCIN doesn't do this for you - so your AD conversion clock is way too fast with ADCON1 = 0 by default.

Thanks, Bruce.

I've used ADC with other devices (12F683; 16F88; 16F1827) and always gotten by with the RC clock.

Can I use DEFINE ADC_CLOCK 1? Or if I use ADCON1=%00010000, do I simply omit the DEFINE?

[Bruce]

Hi Russ,

DEFINE ADC_CLOCK xx only works if the clock select bits are in ADCON0, so just write directly to ADCON1 to set the conversion clock. ADCON1 = %00110000 for RC, ADCON1 = %00010000 for Fosc/8 (recommended).