Hi All,
I think I fried my mbed, but I want to ask here before I shell out for a new one. Here's what happened:
I'm in the beginning stages of a new project. I was using the mbed to read a potentiometer sensor, and implement PID control to a 12v motor via an L298 driver. The mbed was receiving power from my PC, but the motor from a 12v supply with the ground connected to that of the mbed. There seemed to be big noise spikes coming in through the analog input (potentiometer), so I connected a large capacitor from the input to ground in an attempt to smooth them out. Apparently there was some residual charge left over in the cap - I must have previously had it connected across 12v. Immediately, the mbed went dead (not even the status light). Now, it draws about 1.07 amps when 5v is connected to the mbed power pins. When connected to the PC usb, the computer doesn't even register that it is there. I have tried connecting it while holding the reset button - no response.
Any suggestions? Any help would be great.
UPDATE: I have connected 5v across the power pins again to investigate. There is still 3.3v coming from the VOUT pin, but the voltage from the VU pin (5v USB out) is about 500mv and slowly drifts upwards. When the mbed is getting power from the PC, both the 3.3v and 5v outputs seem to show a weird signal - almost like a square wave with a very low duty cycle.
I'm really hoping there is a small IC that I can change and all will be well again.
UPDATE 2: The schematics for the mbed (http://mbed.org/media/uploads/chris/mbed-005.1.pdf) show that there is a "power management" IC on the USB line - the FPF2123. I looked at the datasheet for it and it shows that there is a 160ms reset period during overload conditions. That explains the weird square wave - it has a period of almost exactly 160ms. This shows that it is working correctly. The next thing that I tested was the voltage regulators (the LD1117S33 IC's). The one on the right outputs 3.3v as it should (which explains why the 3.3v pin receives proper voltage when powered externally). The other one, on the left, outputs about 2.5v which is unusual. I suspect that is may be blown (I really hope so, because its the easiest chip to replace!)
Thanks again,
Matt
Hi All,
I think I fried my mbed, but I want to ask here before I shell out for a new one. Here's what happened:
I'm in the beginning stages of a new project. I was using the mbed to read a potentiometer sensor, and implement PID control to a 12v motor via an L298 driver. The mbed was receiving power from my PC, but the motor from a 12v supply with the ground connected to that of the mbed. There seemed to be big noise spikes coming in through the analog input (potentiometer), so I connected a large capacitor from the input to ground in an attempt to smooth them out. Apparently there was some residual charge left over in the cap - I must have previously had it connected across 12v. Immediately, the mbed went dead (not even the status light). Now, it draws about 1.07 amps when 5v is connected to the mbed power pins. When connected to the PC usb, the computer doesn't even register that it is there. I have tried connecting it while holding the reset button - no response.
Any suggestions? Any help would be great.
UPDATE: I have connected 5v across the power pins again to investigate. There is still 3.3v coming from the VOUT pin, but the voltage from the VU pin (5v USB out) is about 500mv and slowly drifts upwards. When the mbed is getting power from the PC, both the 3.3v and 5v outputs seem to show a weird signal - almost like a square wave with a very low duty cycle.
I'm really hoping there is a small IC that I can change and all will be well again.
UPDATE 2: The schematics for the mbed (http://mbed.org/media/uploads/chris/mbed-005.1.pdf) show that there is a "power management" IC on the USB line - the FPF2123. I looked at the datasheet for it and it shows that there is a 160ms reset period during overload conditions. That explains the weird square wave - it has a period of almost exactly 160ms. This shows that it is working correctly. The next thing that I tested was the voltage regulators (the LD1117S33 IC's). The one on the right outputs 3.3v as it should (which explains why the 3.3v pin receives proper voltage when powered externally). The other one, on the left, outputs about 2.5v which is unusual. I suspect that is may be blown (I really hope so, because its the easiest chip to replace!)
Thanks again,
Matt