Debug/Serout/Serout2 - please, need advice ...

[Art]

And if that doesn’t work, just get the chip to tell you what it is

mode var word
mode = 100;
WHILE mode < 60000
SEROUT2 GPIO.5,mode,[ "     ",DEC mode,"     ", $0D, $0A]
mode = mode + 1;
WEND

[Scampy]

Interesting project.

I'm no expert on schematics, but something doesn't sit right with the coms section. The 5v logic is used to turn on the 2n3906 via a 4k7 current limiting resistor. To prevent a direct short R10 is used, with R8 restricting the current drawn through the transistor. Normal RS232 ports like to use 12v not 5v as shown, so wondered if this could be part of the problem. But then in the linked post it must of worked for the OP who designed the volt meter ?? uhmm.

Just for clarity, I would get an FTDI based 5v USB to Serial TTL converter, that is seen as a normal com port by the PC and see if that works... If so then the com1 port on the PC is not getting a true voltage and corrupting the system. In the original schematic there is a 20v max line. If this was 12v and the emitter of the transistor was connected to this line than that might work as it's closer to the normal RS232 voltage levels, but then again - I'm no expert and wouldn't want you to damage the PC.

One other thing you can try - check the com setting in the serial capture program and set the flow control to none... I found that with this set to any other option in many serial terminal programs you get garbage displayed on the screen.

Disclaimer: you follow any suggestions at your own risk.

[fratello]

Thanks for support !
The schematic is "valid" since with the original soft works just fine ... When I "give up" to voltage monitor program (VB) I am unable to receive consistent data.

[Scampy]

Hey, wasn't being negative....like I stated - I'm no expert... if it works with the original code then the hardware is fine....

[mackrackit]

You screen shot shows 300 baud, that is why I gave the example that I did.

Now I notice you code a schematic showing 2400 baud.....

[Art]

RS232 is -12 Volts on the low, so there’s actually 24 Volt difference between one state and another.
I don’t believe it’s possible to do RS232 with any one single transistor if the ground is connected to the other device.

The whole compromise to make 5 Volt RS232 ports is just that.
It could be damaging to connect a real RS232 port to a pic without proper clamping if it didn’t have some awesome IO characteristics.

[tumbleweed]

The RS232 voltage spec:
-3V to -25V = logic 1
+3V to +25V = logic 0


However, if you take a look at a lot of the "MAX232" class chips you'll find that the RXD receiver input has the following characteristics:
Input high threshold: 1.7V (typ), 2.4V (max)
Input low threshold: 0.8V (min), 1.8V (typ)
Input resistance: 3K-7K ohms (pull-down to ground)

Those levels are actually close to what you'd get out of most TTL outputs! It's not "RS232", but you can pretty much drive that directly from a PIC output pin.
I wouldn't do it for a real commercial product, but for a one-of you could probably get away with it.

Connecting to the TXD level from an RS232 output is a different story. There you have to deal with the fact that you might get as much as +/-25V levels on the pin.

[Charlie]

Folks don't get distracted by the schematic. This can work with that schematic, or with a piece of wire from pin 2 of the PIC to pin 2 of the DB-9. The transistor and it's support resistors are not really helping anything, but not really hurting either. The problem will be in the code, or possibly a bad PIC. I remember 12 bit cores don't like SEROUT2 but I'm not sure if this device is one of these?

[fratello]

Thanks for support !
As I say the schematic is fine (I think !) : http://www.picbasic.co.uk/forum/showthread.php?t=7182
Just my program is bad ...