3v input problem....

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Grogster Admin Group Joined: 31/12/2012 Location: New Zealand Posts: 10039	Posted: 05:40pm 31 May 2017       Hello folks. I have a 5v TTL RF receiver connected to COM3 on the E100(via CLICK 1 socket), which is a 3v3 input. The E100 has a 1k series resistor on this line(R11), and all is working fine with the 5v input, but I figured it might be safer to put a potential-divider in front of that input, to keep the voltage within the 3v3 specs, so I built this: ...but I then get no response from the system. The voltage on COM3 RX is 3v0, which is spot-on within spec, so I would have expected it to work? (electrical specs of the manual say a logic-high is >=2v5) I have an E64 where I do this, but it does NOT have the 1k "R11"(just the potential-divider - in that case 2k2/4k7), and this idea works just fine on that one, so it must be something to do with the 1k series resistor, but I can't see HOW this is stopping it. For now, I have gone back to the 5v input on COM3 via CLICK 1 socket. Can anyone offer any explanation, as I am scratching my head at the moment.... Smoke makes things work. When the smoke gets out, it stops!