In my haste to add a capacitor to a breadboard, I didnt bother to disconnect power from the switching regulator and managed to short the output of the regulator, frying the regulator IC, and causing the voltage to rise on the output, from 5V to ~16V.
The 5V rail was at 16V for just a split second.
There was a PIC and the receiver module from the 434MHz link that SFE sells. The PIC was acting weird, and i just threw it out as I’m sure that something was broken with it. I was in the middle of redoing the receiver board, and the receiver functioned fine before I started the switch. I replaced the PIC, and now the receiver does not work (the analog and digital data are 5V no matter what the transmitter is doing).
Is the receiver bad or should I debug the circuit more?
It is hard to say if the receiver is toast, although it is likely that it is fried. If the only change was putting 16v on the rail for a short time (i.e no wiring changes), it would seem that the receiver is dead. The funny thing about overloads is that the results are unpredictable. Some parts can take a severe overload and continue to function for a long time. Others fail immediately, and still others fail after a short period of time. That is what makes repairing electronics after a lightening hit so much fun. What damages most devices is the thermo overload. Under the right circumstances, it only requires nanoseconds/microseconds to raise the junction temperature to a failing point. That being said, I’ve managed to dodge disaster more than a few times.
If you are concerned about an overload in the future, put a 5.6v zener across the power (and fuse the supply). That way, you’ll toast a cheap diode and not your PIC and receiver.
Well, i guess the problem is that too much current was being drawn from the regulator. So adding the zener only protects the pic and the receiver, not the regulator IC. Any suggestions for an overcurrent protection, as i dont think a fuse will do, or will it?
Anywho, what I was trying to get at in the previous post was that I’m not sure that the receiver was functioning correctly on the new board even before the short, which is why I added a capacitor, because I remember having troubles with the ripple from the regulator on the board I took it off of.
I ran the “old” board about a half hour before I started moving components over to the new one, and it worked fine.
Now, it just seems as though the receiver is outputting a constant VDD on the analog and digital out pins.
I’ll hook up an LCD so I can get better error reporting, but from the status LED’s that I’ve put in the code, the receive line never goes to 0v (this is connected to the digital out).
I know the code is partially correct because when i manually pull the rx line low, the PIC turns a corresponding LED on.
You’re right about the zener not protecting the regulator. I haven’t given it a lot of thought, but I know that many regulators have short circuit protection. Perhaps others can suggest a suitable solution. I view the zener much like surge protectors. They’re protecting the high ticket items. Of course if your switcher happens to be a high ticket item…
If you have a scope or lacking that, a LED (and resistor) on the output pin, you should see flickering due to noise in the absence of the transmitted signal. That’s all I can think of at the moment.
Ya, the output is constantly at 5V, the and never varies.
I’m just gonna assume the module is shot, and order some new ones.
Thanks for the suggestion about the zener to protect the devices. Except I’m not sure on how to place it. Does it just go inline with the output from the regulator?
I place the zener across VDD and VSS which means it is toasted on an overload. A fuse on the output of the regulator would be a nice touch, but I was looking for protection for my more expensive components.