Hello,
I’m trying to get the information from Sunny Buddy Solar Charger, is it charging. It’s got a pin called charge, which is low, when the device is charging. This information would than be detected by Redbear Duo (which is Particle with bluetooth). Right now I have just connected the charge pin on Sunny Buddy to digital pin 3 on Redbear Duo, but what I get is a little unstable. I think I should make the connection more sophisticated in terms of electronics. Could you propose some solution?
Datasheet to Sunny Buddy chip:
Github of Redbear Duo:
What should be between pin “charge” on this LT3652 and digital pin on Redbear Duo to get accurate reading?
What do you mean with that?
And the LT3652 datasheet tells this
I designed this charger circuit with LT3652 and it is working fine. It gives me output of more than 1A current.
Hello there, thank you for your help. Still that was not the question. I have a working solar charger which is Sunny Buddy by Sparkfun. I only need to monitor the charging status and this charger has got a special pin for that purpose my question is : can I just connect the “charge” pin on Sunny Buddy to Digital pin on Redbear Duo, or should there be some more parts like resistor in some configuration or else?
For better illustration of my problem here goes a short sketch with the connection in question being highlighted.
Thanks for any help.
According to the data sheet "CHRG (Pin 4): Open-Collector Charger Status Output; typically pulled up through a resistor to a reference voltage.” You can connect it directly to D0, however you need to configure the pin as INPUT_PULLUP, not just INPUT. Or you can add an external pull-up resistor.
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Thank you for the answer. I tired with normal INPUT and the values were “floating” so probably this INPUT_PULLUP will fix this. Will check this, thanks.
Is there any theory behind it? So I could use the knowledge in future? Could you point me to any article or a book? What was my “floating values” problem coming from?
Open collector outputs function such that they are pulled low when active, and essentially disconnected when not active, which is why it appears to float to random values if you don’t have a pull-up resistor or configure it with one. There are a couple reasons you’d do this, but in this case it would allow you to monitor more than one charger from a single pin, essentially the pin would be active low if any one or more of the chargers were charging (pulled low).
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Using an open collector output also allows you to pull-up to a voltage other than the circuit’s own power supply voltage. This is a key attribute of the I2C bus where you can use 3.3v devices but pull-up to 5v to interface to an Arduino for example. The caveat is that the 3.3v device must have 5v tolerant (input) pins. 
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Thank you VERY much. Now not only I know what to do, but also … why:)
Thanks,
Jan
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