You 'suspect' this now from trial and error process of elimination ?
I'm going to check it and see if my result have changed at all. I need this thing to control some pumps right this second so ill have to sit here and watch it until its done. Then I can take it down for a couple hours again
So this is all happening in REAL TIME ?
Sort of. I setup a system around this device and without this device for too long ill have bigger problems. Its between being used and being debugged
do you think 1ft of 22guage is too much for the i2c? i tried to induce much noise around the circuit but it had no effect of my problem. i will let it run with the 2.5k although a bit low must be safer than 500ohm
I also put a .47uf de coupling capacitor on the pcf8574. i already have caps on the 5v rails and 12v rails. I worried. i need to add 2 more pcf8574's to the i2c bus. Does this mean im going to need to change all the pullups on the devices to get the total resistance in an acceptable range? i wish i could measure the capacitance.
I have an oscilloscope but im not sure what i should be looking for as far as phantom messages being received by the pcf8574
Have run the I2V scanner ?
i have not hooked them up yet. im worried about the integrity of the i2c messages. I have run the i2c scanner yes
Would it make more sense to remove the pullups from all the devices and just use 2 pullups total on the arduino side of the i2c?
running it with 500 ohms of much more of a risk
than 2500 ohms
yes you can do that if the value is 4.7k
yeah, that's fine
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anyone know of an affordable meter that could measure the capacitance ranges for i2c?
Could the resistance on the i2c bus being 500ohm cause the pcf8574 to sink too much current and cause a reset?
The exact voltage on the 5v rail is 5.56volts
Is that the arduino 5V pin ?
There's something wrong.
Max allowable voltage for a 5V supply is 5.25 V.
Nick gammon did some interesting measurements.
~50k
33k
10k
4.7k
2.2k
1k
470 ohm
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What exactly am I looking for here. I see faster rise times for lower resistance but what else am failing to see in this picture?
I am powering the 5v rail with a switching regulator. I have decoupling caps and power capacitors all over the rail. Do you think 5.5 is too high? I think the datasheet says its okay
Maybe someone can help me understand this better. With 500ohm pullup at 5.5v, how much / is the pcf sinking/sourcing current on the i2c bus pins?
From what I've read, when you reset/power on the pcf8574 all the pins are set to high state?
I'm wondering if maybe the 500ohm resistance on the pcf8574 i2c bus caused it to reset somehow From sinking/sourcing too much current