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PCF 8575C Problem  [SOLVED]

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Post Number:#1 Post Wed Jun 13, 2018 6:07 am
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Hello,
today I tried to connect the PCF8575. The problem is that the HIGH level on the output is just about 1.6V instead of the expected 5V.
A0,A1,A2 is connected to ground. R1-R3 are 10k resistors.
Does someone know what's the issue?

Post Number:#2 Post Wed Jun 13, 2018 10:27 am
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Hi!

The voltage is around 1.6 V on PCF pin when there an ULN connected for this.

Remember that the signal is LOW (GND) in ULN output pins.

Best regards.
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Post Number:#3 Post Thu Jun 14, 2018 2:29 am
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Okay great. I thought that the HIGH level is 5V
Yes I know it's an NPN darlington transistor
Thank you :D

Post Number:#4 Post Thu Jun 14, 2018 5:05 am
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The transistor doesn't open completly when PCF is connected. So i measured the PCF output pins with a oscilloscope and found out that it isn't 1,6V, it just have 5V peaks.
I measured P5-P9 why aren't they constant on HIGH? The timer is turned ON in display

Image


regards Yannick

Post Number:#5 Post Thu Jun 14, 2018 11:10 am
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Hi!

I haven't an oscilloscope.

I just can say that the voltage in PCF pin is 1.6 V with ULN connected and 5V disconnected.

Which type of device you are trying to control?

Best regards.
Post your doubts on forum because it can help another user too. Just PM me for support if it's absolutely necessary.

Post Number:#6 Post Fri Jun 15, 2018 9:04 am
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Okay I thought someone knows why the signal look so wierd like this . I will try to use an other IC at monday

Have a nice weekend and thanks for quick response :)




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