12F683 - basic code not working

[HenrikOlsson]

Hi,
Glad you've got it going! Just a quick note: The I2CREAD/I2CWRITE commands does not use the (M)SSP module in the PIC. You're enabling the (M)SSP module for I2C mode so I'm actually a bit surprised that it works because I thought that when enabled it (the (M)SSP module) takes control over the I/O-pins - I'm obviously mistaken there.

However, the PBP I2C commands are bitbanged, they don't use the I2C hardware in the PIC so there's no need to enable the hardware for it. It might lead to problems.

/Henrik.

[Scampy]

Thanks Henrik,

So I can remove the SSPCON line ?

[HenrikOlsson]

Yes, according to the datasheet the POR default of the SSPCON register is 0. Looking at the register definition it shows that as long as bit 5 is 0 the SSP module is disabled and its pins functions as normal I/O. This is probably also why it works the way you currently have it - you do have it configured for I2C mode but it's not actually enabled since bit 5 is cleared. Had you enabled it I don't think the I2C commands would've worked since the SSP module then would've been in control of the pins.

/Henrik.

[Scampy]

Guys,

I've been resting my code using a DC motor driven by a simple transistor circuit as per attached which works well, with the intention of using a double pole change over relay to switch the polarity to the motor (throw off from my old model railway days as that's how we used to make the loco go backwards or forwards). The think is I can't get my head round how to use the transistor to turn the power on / off.

I came up with the attached, but not sure if this would work, or if I should have the transistor between the relay and GND (ie C to relay, E to GND). I've left the Diode out as the motor is bi-directional

Advice welcome before I blow up a handful of transistors trying

[pedja089]

I use this for motor driver:

[Scampy]

Thanks you..

[HenrikOlsson]

Hi,
Regarding your first schematic, generally you need to put the transistor on the low side. Otherwise you need a higher voltage on the base than you've got on the collector. Put the relay "on top", then on to the motor and finally the transistor at the bottom, emitter to ground. Yes, the motor is biderectional but the current thru the transistor is always the same so put the diode back across is, cathode facing "up" of course.

/Henrik.