Stokerkontrol 3.50beta alfa3

[nordgren.dk]

Hej Jens
Håber du har planer om at bruge Påsken til et ny Linux program (som lovet) Så vil jeg til gengæld udføre en lille test, om vi kan undgå USB adapteren. Det bør være muligt at kable styring direkte med Raspberry, ved blot at benytte den seriale port. Det ser enkelt ud og det skulle være tilstrækkeligt at benytte et kat 5 kabel til opgaven. Se foto af TX, RX samt GND på begge enheder.   

[BoinkUser]

Hej Jens
Håber du har planer om at bruge Påsken til et ny Linux program (som lovet) Så vil jeg til gengæld udføre en lille test, om vi kan undgå USB adapteren. Det bør være muligt at kable styring direkte med Raspberry, ved blot at benytte den seriale port. Det ser enkelt ud og det skulle være tilstrækkeligt at benytte et kat 5 kabel til opgaven. Se foto af TX, RX samt GND på begge enheder.

Hej Klaus

Ja det skulle være muligt at benytte seriel porten. Porten hedder formentlig /dev/ttyS0.

Dog skal du være opmærksom på at den kører TTL, så der skal bruges en level shifter, for at kunne kommunikere med en PC.

Der er nogle der har rodet med det her f.eks.:
http://www.savagehomeautomation.com/projects/raspberry-pi-installing-a-rs232-serial-port.html

Tilføjelse: Nå det er jo Linux, så helt nemt skal det jo aldrig være. Porten er optaget, da den bruges som consol til operativsystemet, der er nogle der skriver lidt om, hvordan man frigør den her:
http://www.irrational.net/2012/04/19/using-the-raspberry-pis-serial-port/

Hvis du får liv i den skulle vi måske lave en lille blog, der beskriver, hvordan man nemt får den slået til og installeret level shifter.

Mvh. Jens

[motoz]

Jens, what are the logic levels of the internal serial bus in the V6 box? Probably 5V I guess, but if its 3,3V it would be neat to just rip out the level converter from the V6 box and connect directly to the rasp's 3,3V port without using any level shifter.  I've been meaning to check it out sometime but I guess I can just ask nicely instead :-)
/Anders

[BoinkUser]

Hi Anders

Its 0-5V before level shifter on the v6 control box, you can check out specification for Raspberry, some 3,3V devices have no problem with a 5V signal, but if its not designed that way, you might damage it.

Regards Jens

[motoz]

Thanks, 5V will definitely burn out the rasp's input but still it could be done with only one 3V-5V level shifter instead of two rs232 level shifters in each end.

Or as I suspect the control box will accept 3,3V as active input, probably all that's needed is a resistor and a 3,3V zener diode to protect the rasp's input.

[BoinkUser]

Thanks, 5V will definitely burn out the rasp's input but still it could be done with only one 3V-5V level shifter instead of two rs232 level shifters in each end.

Or as I suspect the control box will accept 3,3V as active input, probably all that's needed is a resistor and a 3,3V zener diode to protect the rasp's input.

Theres a good chance the controlbox will accept the 3,3V input, try it :-)

Regards Jens

[nordgren.dk]

Hi Motoz. Er enig i at vi skal undgå 2 x r232. Så vil tilgå V6 styringen direkte. Men kan ikke finde et diagram over montering af 1 stk. modstand på 10 kohm samt 1 stk. 3,3 volts diode. Har du et link eller en forklaring. På forhånd tak Klaus

[motoz]

Google found a nice picture: http://i2.wp.com/jamesreubenknowles.com/wp-content/uploads/2013/03/strategy11.png?resize=375%2C181

A zener diode has a more or less constant voltage drop in the 'back' direction, so you get a diode manufactured with the required voltage drop and add a resistor to limit the current to a suitable level. In this case the load on the 3,3V side is negligible so any resistor in 10kOhm - 50kOhm will probably do just fine.

And since the input does not have to be exactly 3,3V  you could also just use a voltage divider to lower the voltage to a safe level, but a zener is the safer alternative since it also cuts voltage spikes from possible disturbances. Also a ttl level connection is much more susceptible to disturbances so the cable need to be as short as possible with good ground connection in both ends, and possibly shielded.

[nordgren.dk]

Hej Motoz
Super hurtig svar TAK. For at undgå jeg begår fejl. Når jeg har de 3 ledninger fra styringen V6.
TX
RX
GND
I hvilken ledning skal jeg indsætte modstanden ?
Mellem hvilke ledninger skal dioden sættes og i hvilken retning skal den spærre ?

[motoz]

Like this:

Kode: [Vælg]

                +––––––––––+                             
V6-tx  +––––––––+    R     +–––+––––––––––––––––+  RASP-rx
                +––––––––––+   |                         
                               |                         
                               |                         
                         |     |                         
                         +–––––X–––––+                   
                              X X    |                   
                             X   X                       
                            X     X                       
                           X       X                     
                          XXXXX+XXXXX                     
                               |                         
                               |                         
  GND  +–––––––––––––––––––––––+––––––––––––––––+  GND   
And make sure that the diode really is a 3,3V zenerdiode, a 'normal' diode in that connection will not draw any current and the rasp will get 5V and burn out. Note that a zenerdiode also works as a normal diode ie. leading current in one direction and blocking in the other, with the difference that it has a low and defined breakdown voltage in the blocking direction and that it does not burn out when the breakdown voltage is exceeded as a normal diode would do. So a zener diode is normally used backwards, ie current is passed in the blocking direction making used of the sharply defined breakdown voltage level in that direction. And you need to pull out the max232 chip from the V6 and check it's pinout for which pins to use.

[nordgren.dk]

Har forstået med modstand og diode. Køber flg.:
https://www.elextra.dk/main.aspx?page=article&artno=H12955
&
https://www.elextra.dk/main.aspx?page=article&artno=H14024
er det ok ?

[motoz]

Yep.
Hope this works, it's a bit backwards that the usb-serial converter costs almost as much as the raspberry so it would be nice to be able to skip it. If 3.3V turns out to be too low for the rx-input of the V6 then there are lots of ways to levelshift that to 5V, but hopefully not needed.

[nordgren.dk]

Hi motoz. Just found this on eBay:

http://www.ebay.co.uk/itm/Pi-RS232-cable-Raspberry-Pi-Pi-Console-cable-/320953086488?pt=UK_Computing_Internal_Port_Expansion_Cards&hash=item4aba4b7218

Will this protect my Raspberry from getting more than 3,3 V ?

[motoz]

I would hope so as it is advertized as a raspberry pi console cable. Hard to see from the picture but the connector should connect to 3.3V, GND, RX and TX. It should have a max3232 (or similar) chip to work with 3.3V supply, max232 apparently needs 5V so it doesn't work. Did you try with a zener diode? I was going to try myself, but i think I'll wait until summer starts for real.

[nordgren.dk]

Haven't tried yet. Have the Zener diode  inhouse.  Have  ordered one http://m.ebay.com/itm?itemId=141268615846 witch I am planing to fit outside my Raspberry pi box. This gives me the possibility to install the Zener diode to. And I am still waiting that Jens make a new Linux program.