GPS NMEA, Failover Circuit upgrade attempt.

[Sadlercomfort]

I think the negative pulses will be okay, since no mention of this in the Picaxe data sheet.

I do think a diode is needed for GPS #2 on B.1 Pin to protect the Picaxe.

C.5 Serial In pin already has an internal diode.

 

[HellasTechn]

Ok. What i dont understand in the above circuit is the purpose of D1 and why is its cathode connected to +5V.

also one minor detail would be that the relay will only need to switch the data pins (+) the return pin (-) will be common for CN1, CN2 and CN3 and transistors will not be needed since current required will only be a few ma.

 

[Sadlercomfort]

The diode will not conduct if the serial input is less than 5V. But if the serial swings higher than 5V the diode will conduct and clamp the voltage to 5V.. protecting the picaxe.

I didn't know the return pin (-) was common but the transistor is still needed to switch the relay right?

 

[HellasTechn]

but the transistor is still needed to switch the relay right?

No i dont think so. I will have to check to make sure but i think it will not need more than 50ma.

The diode will not conduct if the serial input is less than 5V. But if the serial swings higher than 5V the diode will conduct and clamp the voltage to 5V.. protecting the picaxe.

An 7805 will do the job just fine. there will be no need for that diode.

 

[Sadlercomfort]

No i dont think so. I will have to check to make sure but i think it will not need more than 50ma.

Note that the picaxe datasheet states that it can sink and source up to 20mA.

An 7805 will do the job just fine. there will be no need for that diode.

Yes your right, of course

 

[CDRIVE]

On the 14M2 physical Leg 2 (C.5 Serial In) is the Program Download pin. It can be used as a Serial RX pin but with caveats. The Picaxe PDF manuals cover these issues.

For complete descriptions of these commands refer to the PDF Manual 2 (Basic Commands).

hSerIn
SerIn
SerRxd

Chris

 

[Sadlercomfort]

Two Serial inputs are required here, C.5 and B.1

 

[HellasTechn]

Does that look OK ?

 

[HellasTechn]

In the above picture i forgot to mark pin 5 of the DB9 connectors as GND and the same for com pin of the 7805

 

[CDRIVE]

Your LED's Anode-Cathode is reversed and it's also missing a limiting resistor. Also, you can't feed a 5V regulator with 5V input.

Chris

 

[davenn]

Your LED's Anode-Cathode is reversed and it's also missing a limiting resistor. Also, you can't feed a 5V regulator with 5V input.

Chris

yes ... exactly ... just a few problems there

you will need bare minimum of 7V into the reg but preferably 8V +


Dave

 

[HellasTechn]

Here is a new diagram.

 

[HellasTechn]

Your LED's Anode-Cathode is reversed and it's also missing a limiting resistor. Also, you can't feed a 5V regulator with 5V input.

Chris

yes ... exactly ... just a few problems there

you will need bare minimum of 7V into the reg but preferably 8V +

Thanks !

 

[CDRIVE]

Why did you remove the protection diode across the relay coil?

Just a tip when posting schematics:
It's good practice to label components, IE... Rn, Cn, Qn, etc. This way we can more easily reference them in our replies.

Ash, I see you've put considerable time into this topic. My apologies for being very late to the party. Especially since it appears you didn't need any help.

Chris

 

[HellasTechn]

Why did you remove the protection diode across the relay coil?

By mistake. It's ok now.

Ash, I see you've put considerable time into this topic. My apologies for being very late to the party. Especially since it appears you didn't need any help.

Yes he has !!!

Thank you both !

 

[HellasTechn]

Afrer reading Picaxe manual 1 i see that they do not use transistors to drive LED's so i assume the new diagram without the transistors should be ok.

What do you think ?

 

[davenn]

Here is a new diagram.

one last thing ..... a serious omission ... you show lines crossing and others that are "T" joints

you MUST mark those that are actual joint else no one knows where there are or are not joints

eg .....




this is absolutely critical,


cheers
Dave

 

[HellasTechn]

one last thing ..... a serious omission ... you show lines crossing and others that are "T" joints

you MUST mark those that are actual joint else no one knows where there are or are not joints

Yes that is correcty but if you take a really close look you will notice small dots at "t" joints.

They should be bigger i know but it is the drawing software i use....

 

[davenn]

Yes that is correcty but if you take a really close look you will notice small dots at "t" joints.

They should be bigger i know but it is the drawing software i use....

then you need to add them by hand later

and what about all the crossing wire .... intuition tells me some of them are jointed and some are not
but it is totally unknown by your diagram

you need to sort that out .... it has to be made really obvious

 

[HellasTechn]

It is now Thank you for pointing this out.