i use an UNO, and loving it.
my question concerns incorrect/variable readings with LM35's.
i have used example sketches to help smooth/average readings taking but my issue may be other.
i have 3 sensors with up/down buttons to control on/off temp for fan relays displayed on lcd
i have 3 separate boards: paralleled power from wall unit before final install in truck board 1 contains:
12VDC in with 7805
3 relays each driven with 3904
3 LM35 sensors on 24" leads mounted to aluminum casing of audio amp
board 2 contains:
12VDC with 7805
standalone 328P with 16MHz crystal
3 led outputs to board 3
3 relay outputs to board 1
3 temp inputs from board 1
button read input from board 3
20x2 lcd ribbon to board 3
5V supply to board 3
board 3 contains:
20x2 lcd with 10K pot
6 buttons on resistor ladder
everything works great except when i test the set limits on the LM35's.
if 1 relay kicks on, the temp readings for all 3 jump 2 degrees. kick in another realy, up 2 more degrees and 3rd relay, up 2 more degrees. readings drop as relays turn off
the initial temp from LM35's is fairly accurate comparing to a separate temp unit i have.
i can check voltage at lm35 and it varies by .01v when relays kick in and out.
i have tried internal ARef with 1.1V
i have used external with 5V
i have seperated lm35 grounds
all above still get jump when relays kick in.
i will upload .ino and/or .sch files if someone would like to verify
not that it is all that important but it is killing me not knowing what is going on and why
You need to separate high current ground wiring that's taking the relay current
from the LM35's and the Arduino that's sensing them. What is most likely happening
is that your ground reference is changing as the current through the shared ground wire
changes. Its crucial that the high currents do not go into the Arduino board at all, but
stay confined to the loop between supply, relays and transistors. There should only be
one connection from the high current ground wiring and the Arduino ground.
not sure if i understand how to do since the the ic uses separate gnd pins but are still the same gnd.
do i need two separate ground leads and separate that way? one from battery source for relays and one from 328p for temps?
i am attaching pics of my boards and a sketch of how i have power now.
constant power to retain settings when in pwr_down sleep
grnd parrelleled
switched 12V for sleep function parrelleled
another question:
for what i have experienced in the electrical industry i dont believe it will have any effect on the boards/power but when i have the fans connected with external power (24V) at the NC-C-NO terminals, that power should not travel into the circuit to cause issues, correct?
You need to separate high current ground wiring that's taking the relay current
from the LM35's and the Arduino that's sensing them. What is most likely happening
is that your ground reference is changing as the current through the shared ground wire
changes. Its crucial that the high currents do not go into the Arduino board at all, but
stay confined to the loop between supply, relays and transistors. There should only be
one connection from the high current ground wiring and the Arduino ground.
1.) after looking on the web for solutions, it seems that i need to do ground planes on my boards which talk about A/D signals.
from what i gather and by quote above, i would need two planes joined close to regulator: 1 for temp sensors and 1 for relays. sound correct???
2.) also read about ferrite beads to separate signals from analog/digital.
would i need to use some of these even though i am not dealing with RF signals?
does it hurt using the beads anyway?
realized i need to add some decoupling caps at ic, easy to do but my question is 1 or 2?
VCC/GND and AVCC/GND.
i am thinking 2 since they are on opposite sides.
since they are on opposite side, is 1 digital and 1 analog? (AVCC being analog?)
if so, is that where the A/D separation is coming into play for ground planes.
