Re: ATMega16 Interface with SSR

On Mon, 28 Jan 2008 13:44:29 -0800 (PST), in sci.electronics.design
linnix <me@xxxxxxxxxxxxxxxxxx> wrote:

On Jan 28, 1:11 pm, Martin Griffith <mart_in_medina@xxxxxxxx> wrote:
On Mon, 28 Jan 2008 12:53:37 -0800 (PST), in sci.electronics.design



JoeyB <joseph.bur...@xxxxxx> wrote:
Hi All,

I've got a ATMega16 that is interfaced to a LM34 temperature sensor.
I'm using the ADC noise reduction (sleep) mode every second when I
sample my ADC. Based on the temp, I'm TRYING to drive a SSR directly
from the micro on Pin B0. The micro has a 300 ohm impedance that
should limit current to 16ma @ 5VDC. This is an acceptable load for
the micro. The only onther load is a LCD. I've done other projects
with this SSR and the mega16 albiet simpler - never a problem - the
Mega16 can source enough current to drive this particular SSR when it
is the only thing hooked to it. Now, when the micro determines that
it needs to turn on the SSR, it puts out 5VDC to the pin. With the pin
disconnected, no problem, 5VDC. When the pin is connected to the SSR,
the voltage on the pin is only 1 VDC. I put an ammeter in series with
the pin and the SSR and measured .1ma. So, it looks like the pin is
only sourcing 1 milliwatt of power...? According the the data***, it
should source 20ma@5Vdc.
Anybody have a clue? The micro is going into sleep mode and
taking measurements while it is trying to drive the SSR. Is this the
problem? Can the micro drive pins in sleep mode? I'm assuming my power
supply to the micro is sufficient because my VCC stays at 5VDC with
the pin at 1VDC. I've tried a couple of different SSRs. I'm pretty
sure they're ok. I've switched the output from Pin D0 to Pin B0, no
luck there. I've got the pins configured as outputs, DDRB, DDRD set to
1. I shouldn't have to worry about pullups when the pins are
configured to be outputs right? At least, that's what I'm getting
after reading the Mega16 data***. I've triple checked the circuit,
it's wired right...My last resort will be to re-design the circuit to
sink current rather than source it but - IN THEORY - what I have
should work. I can also spend some time taking the noise reduction
sleep mode stuff back out it that's the problem.

Any help is appreciated.

Next time take a deep breath and dont post too much info.
see
atmel doc2545, p330 ( wish it had an index)
shows that you can sink quite a lot of current .

Not in Noise Reduction Mode. The core and I/O module are shutdown in
NRM.


How are you wiring the SSR, between 5V and the port pin. This is the
usual way

or between the port pin and ground?

Either way should be fine, as long as the I/O module is active.


martin
Ah, the finer points of data sheets, thxs, just about to start with
avrs


martin
.