:: 5v SUPPLY - My PIC Doesnt Like It ::

[suby786]

You may have read on the 2nd page about common grounds, i have realised this is NOT THE CASE and is NOT the problem... the difference between powering my BREADBOARD via my USB powered programmer, and my AC->5V supply is this..

my USB power from the programmer is 4.2v... the voltage from MY AC/SUPPLY is 5v... the PICs work, but sending data from the PC through a MAX233A DOESNT WORK... its hard to tell which bit doesnt like the 5v, is it the PIC Rx pin or is the MAX233A (both of which have 5v in its NORMAL OPERATING RANGE...

I have confirmed this by plugging an off the shelf 5v supply to the board, with NO COMMS... i plug in my ac supply that gives 5v from the reg and i get no comms, IF I wind down the variac 2 my PSU... so that the rectified signal thats fed into the 5v reg is lower, and so ill get 4.5v out the reg...THEN and ONLY THEN will i get comms and everything works

ANY IDEAS why my electronics ONLY work < ~4.5-4.6 VOLTS

and NOT on 5v?

HELPPP

 

[penoy_balut]

check for power contention in your circuit

 

[suby786]

hey mate

ive searched for power contention but no understandable results... what do you mean by CHECK POWER CONTENTION?

Please explain further, this thing is holding me up its soo annoying. How odd is it that it doesnt want to work @ 5V but @ <4.6/4.7V...

i didnt know 0.3v could make such a difference...

 

[tunedwolf]

I seem to remember asking you to check that you were not laying down a supply to your USB...going from what you're saying here, it's likely you are...

Given the voltage differential, I would assume that your serial port is what is giving you trouble, it is probably swinging far enough out one way, but not the other to be recognised as a proper level, hence no conversion from the 233...

 

[penoy_balut]

power from different sources should have common ground only while their positive rails , either signal or power, should not connect any time and any where in your circuit.

 

[suby786]

its hard 2 understand this..as i dont have ANY OTHER POWER source connected at the same time...its either powered SOLELY by the ICD2 connector or via AC powersupply..

The programmer im using does not have a 5v regulator on board... and without the breadboard connected, its 4.7V... when i connect the connector to the board, the board voltage DROPS to 4.55V.. (with BOTH pics off..) with both pics ON...the voltage drops to 4.4V.

Does this help any further?

 

[suby786]

ok a new revalation... when i REMOVE a wire that connects my USB-SERIAL converter GND wire...i.e. pin 5 of the 9way to my breadboard so that the RS232 has a reference, then my voltage DROPS further to 4.13V... and i get NO COMMS when im using my AC supply, BUT i STILL get comms with no GND wire and powered by ICD2. Remember the USB-SERIAL dongle is POWERED by USB obv so the GND pin 5 (should) be connected to USB GND.. and maybe as my AC GND is (floating) it may not like this?

when i reconnect the wire, the voltage returns to 4.3V-4.4V... and continues working from then with both supplies...

 

[penoy_balut]

you said both PICs, are you using two? if so, are they driving a common data line? if still so, this is where contention comes in, i mean, when the other PIC is pulling the line low the other is at high state, if this is your circuit then you have to use the open drain output pins

 

[suby786]

the two PICS run seperate things... WITH THE EXCEPTION OF same + and -, and have BOTH Rx pins TIED TOGETHER... which go off to t he single wire from the usb>serial adapter... this is the only common dataline... the Rx pin is an INPUT hence if 1 pic is off, it should effect the other pics Rx...

but the same happens with BOTH PICS ON... any further help? i dont see how im puttin power down the SERIAL LINE...

helpppp

 

[tunedwolf]

Have you managed to get a schematic together yet ? I think without one, nobody here can really help you much further. It's going to be easy from this point onwards to get confused about what we are all talking about without having something in common to see...The schematic doesn't have to be pretty, a hand drawn one will be fine as long as it's clear, but it has to be accurate obviously.

 

[Nigel Goodwin]

but the same happens with BOTH PICS ON... any further help? i dont see how im puttin power down the SERIAL LINE...

If you're feeding more than 5V into an input pin, then the protection diodes will shunt it to the Vdd rail.

But your descrptions are too vague, draw a circuit and post it!.

 

[suby786]

i will post a schematic... but i need to find suitable software to do it..

i use PCB proteus f or PCB making... but does any1 know any good schematic software with relative ease to create schematics?

 

[jimg]

I have been looking for a schematic program for the past 2 weeks. Since this is only a hobby, I can't justify spending too much for one.

The free ones come in two varieties, unlimited and commercial programs with a free demo limited to the number of pins you can have.

The best unlimited free ones I have found are:

TinyCad - come with source code if you speak C++ its OK but has poor keyboard support which I prefer for rotating components. The most frustating thing for me is that it is rather metric centric and I think in inches. It will work in inches but the grid never quite lines up. This is the one I think I will continue using.

ExpressPCB - but it puts a ton of stuff in your registry, and doesn't show the component while you are dragging and dropping it.

For the limited ones:

DipTrace - demo version quite good but limited to 250 pins. Has good keyboard support.

Rimu schematic by Hutson systems - This is my favorite, but the demo is limited to 100 pins, and at $150 for the unlimited version is way beyond my budget.

 

[hjames]

I've been messing around with the free demo version of

**broken link removed**
**broken link removed**

I've only been using it to draw schematics for screenshot purposes, so I don't know how useful the simulation or layout is (or what limits it has).

 

[suby786]

Problem fixed,

i had a Rx and Tx LED connected to the input transmission line (ttl line from max chip)... the resistor value was too low and was providing too much V+ to the transmission line,,

its sorted now... my whole board functions @ 5v now happily

 

[tunedwolf]

congrats on finding the troubles...

 

[suby786]

thanx tuned wolf... you helped me a great deal even though the problem was staring me in the face...

hope this site helps me further with other issues...