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I suggest that you simply remove the on-board PTC fuse to cut off the path from the DC-DC converter to RPi. This way, RPi is completely powered by microUSB cable, while 24VAC will still power the sprinkler valves.
Hey Ray (or anyone else that can help),
Where is the PTC fuse? Any schematic or picture I can refer to? I have hardware version 1.42.
Also, if I do remove/disconnect that fuse will the 40 pin header (additional header on the OSPi) still have 5VDC?
Thanks for the help!
I think I found it. Is it the fuse circled in the second image?
If so, can I remove that fuse, then connect the two contact points on the right to carry 5VDC from the pi thru to pins 2 and 4 on the 40-pin header? Am I reading the schematic correctly?
(As an aside, how do I add local photos inline within these posts?)
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Yes, that’s the fuse. You only need to remove it, there is no need to make further connections. The reason is that if you are going to power RPi microUSB cable, that already provide 5V. If you are planning to use a separate 5V adapter (i.e. not through USB cable), then you can solder the +5V wire to the right pad of the fuse, because that’s the side that goes to RPi’s 5V pin.
Okay, on to plan X?
I think I’m going to mount the iQaudio DAC+ directly to the pi:
With the DAC mounted on the pi, my power issue I think becomes moot. The iQaudio DAC has a separate header, similar to the OSPi. If I understand the GPIO pinout correctly, can I just jumper/ribbon cable between pins 3, 5, 7, 8, 9, 10, 11, 13,15 on each header (i.e, DAC header <—–> OSPi header)?
The only pins that the DAC AND OSPi both use are 3 & 5 (as well as power pins), which can both be shared, right?
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I did go with plan X. I soldered a header on the DAC, and the OSPi, and just used jumpers between the pertinent pins.
I did end up with a “ground loop” hum through my 12 volt app. I did not have that with just the pi and DAC. It only happened when the OSPi 24VAC power was plugged in. I solved it by connecting a ground between the DAC and OSPi (pin 9), then also, from the OSPi (pin 39) to the ground of the AMP.
Works great, now 😎!
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