Added by jason almost 11 years ago

Hello. I'm new here, and wanted to say hi first. I'm "fixing" a cheap K40 machine.

Now, the question:

I'm getting 3.5V instead of 5V on my mbed pins. Any idea what I did wrong?

A brief history of how I got here:

I rushed through the assembly instructions populating pretty much everything but C13 & C14 (I have an LPCXpresso board, but that's another project perhaps).

When testing, I had an underpowered 5V supply so I had to go back and double check things. I then realized I shouldn't use R10 & R11 since I'm not using J14 (for not) - so I cut those.

I now have a better supply of 5V (connected to J38), and the green LED comes on, but mbed pins 2, 9, and 10 show 3.59V

I don't have jumpers on for end stops or sensors (but I think I want 5V for the K40 machine right?)

Thanks in advance for any tips.


Replies (2)

RE: 3.5V - Added by jaap almost 11 years ago

Hi Jason,

If you get 3.5V where you should get 5V, you have probably installed the 7805 regulator.

The 7805 is an optional component, meant for systems that do not have a +5V power supply.
If you supply +5V input on pin 3/VAA of J5, you should replace the 7805 with a wire that connects the two outer poles (make sure it's isolated from the middle pole, that's the GND).

RE: 3.5V - Added by jason almost 11 years ago

Yup, that was it. Removed the 7805 and now I've got 5 volts.

Thanks Jaap.

I guess I misunderstood and thought that would give me a stable 5V if I had it there.