Board Killed Prop, anyone see a problem..
rwgast_logicdesign
Posts: 1,464
EDIT: Post 3 contains more info, board pics
Ok so I was just testing out a board I've been making and all the sudden everything went down hill real quick! I have a DS1307 and was trying to check out the Square Wave output with a Scope. The whole board was functioning fine and the clock was keeping the time just like it should. For some reason the Square wave generator was not working right when I set the pin to High it output .4v and when I set it low it output .7v, never mind getting a working square wave.... Anyways I rechecked all the wiring and it looked fine, so I tried to add a 10k pull down to see if that would fix the problem. Well I accidently added the 10k between ground and a no connection pin. So basically the I just had the scope connected to ground through a 10k resistor... well when I powered the prop back up i started getting a RAM CHECKSUM error out of nowhere. I've tried other chips and this chip in other boards, with different code, this is how I know this problem is isolated to the chip. Interestingly I found that I did not have all the power off when I added the pull up, for some reason when my prop plug is plugged in it sends 2.3v through the whole 3.3v rail on the board, im not sure why... Anyways I labeled a picture of the board a long with where I added the pull up and scope before the chip blew, hoping it would make it easier for you guys.
Im running pretty low on Prop Chips now, So I'm hoping maybe the chip is still usable and this problem can be fixed, the prop tool detects the propeller just wont program it due to the RAM CHECKSUM error. I'm also hoping maybe someone could tell my why I'm getting 2v on my board when I have the prop plug connected, this has never been an issue with any board I've built that have on board regulators, and maybe what happened to my Prop so I don't kill another one!!!!!
I searched the forums for RAM CHECKSUM but didn't find a similar situation...
Ok so I was just testing out a board I've been making and all the sudden everything went down hill real quick! I have a DS1307 and was trying to check out the Square Wave output with a Scope. The whole board was functioning fine and the clock was keeping the time just like it should. For some reason the Square wave generator was not working right when I set the pin to High it output .4v and when I set it low it output .7v, never mind getting a working square wave.... Anyways I rechecked all the wiring and it looked fine, so I tried to add a 10k pull down to see if that would fix the problem. Well I accidently added the 10k between ground and a no connection pin. So basically the I just had the scope connected to ground through a 10k resistor... well when I powered the prop back up i started getting a RAM CHECKSUM error out of nowhere. I've tried other chips and this chip in other boards, with different code, this is how I know this problem is isolated to the chip. Interestingly I found that I did not have all the power off when I added the pull up, for some reason when my prop plug is plugged in it sends 2.3v through the whole 3.3v rail on the board, im not sure why... Anyways I labeled a picture of the board a long with where I added the pull up and scope before the chip blew, hoping it would make it easier for you guys.
Im running pretty low on Prop Chips now, So I'm hoping maybe the chip is still usable and this problem can be fixed, the prop tool detects the propeller just wont program it due to the RAM CHECKSUM error. I'm also hoping maybe someone could tell my why I'm getting 2v on my board when I have the prop plug connected, this has never been an issue with any board I've built that have on board regulators, and maybe what happened to my Prop so I don't kill another one!!!!!
I searched the forums for RAM CHECKSUM but didn't find a similar situation...
800 x 600 - 138K
800 x 600 - 55K
Comments
Sounds to me like one of your propeller output pins is directly connected to ground or something.
Maybe when the Prop boots, it makes this pin a high output...
Maybe that is what is dragging down the power supply...
Anyway, I'd double check your wiring...
Obviously Red is Power green is ground
Simple reason is that the transmit output from the Prop Plug idles at 3.3V and it is connected to the Prop RX pins. The Prop Plug TX "signal" ends up being steered through the substrate "protection diodes' onto the supply rail but because the Prop Plug's TX is a signal line it only has limited drive and the voltage falls. Since the Prop is held in reset by the "brown-out" it doesn't require much current and so it maintains this voltage. Trying to put a 3.3V power source directly onto the Prop pin will definitely result in it's destruction as the substrate diode (There are "diode" structures at every P-N junction of a silicon substrate) is not designed to handle anything more than a few hundred microamps. What you are seeing is common to all ICs so you must view all signal sources as low current power sources that can end up appearing to power the equipment by itself. If you want your equipment to be completely powered off you must disconnect the signal sources as well or else design it in such a way that these signal sources cannot flow onto the power rail (i.e. NPN on the receive line).
When you say "I checked my other boards" does this mean you plugged the prop from this board in to the other board and the 3.3V supply was OK?
If the answer is yes the prop chip is ok and the problem is on the board, otherwise the prop chip is bad.
If the prop chip was good the board may have a short on it or may be drawing more current than the supply can handle.
When you are building a circuit the first thing you should do is to draw the schematic with all the components like they will be mounted on the board.
The IC pins should be labelled and numbered.
Transistor type and EBC pins connections marked.
Polarity of capacitors, diodes etc should be indicated.
Now the and connections should be drawn in to make it easier to wire the board. Once you have everything connected you should use an ohmmeter to verify that each power connection goes only to the pins it is supposed to connect to. Then do the same thing for all the signals.
At this point, and before you plug any chips into their sockets, apply power to the board and use a voltmeter to verify that power goes only where it is supposed to go. Once this has been done power down the board, insert the chips, and reapply power.
Your layout and wiring is very neat so it may be that you have a wiring error, reversed electrolytic capacitor or something similar if the prop chip is ok.
Paint is very handy for laying out prototype boards like this. You can lay out the board from the component side and when done copy, paste, and flip horizontal to get the bottom view as well.
I designed this board to be directly powered from switching supply I built on a separate board, I need to adjust the voltages on that board to be .7v higher so I can add diodes on this board in order to properly protect from reverse voltages.
@Peter, thank you for that explanation, do you think that the amount of power from the prop plug is enough to damage the propeller or other chips if its pluged it and you accidently short your board somewhere or something like that? I just figured out why my other home made board does not have this issue, on it, the prop has its own 3.3v regulator! I guess what is happening is the Prop Plug is probably powering the 3.3v rail on that other board it just does not effect anything since the propeller has its own isolated rail. This is the first board I have built where the prop did not have a dedicated regulator and shared the 3.3v rail with everything else, that is probably why this is the first time I have experienced this problem!