Can I leave out the serial plug?

120ThingsIn20Years

Senior Member
If I'm making a run of devices*, and none of the people that will have the devices will be re-programming the chip, I figure I can just program the chips on my prototype, then leave out the plug on the other devices.

The question is, how do I tie down the serial-in pin when there's no plug?

pin -> 22k resistor ->10k resistor -> ground?

Or do I just need the 10k resistor?



Also, I have a few salvaged caps and was wondering what the criteria is for the cap that goes between the + and - to the chip that I think is there to stop power spikes.





*(just a simple overheating alarm with only a few lines of code, a thermistor, and a pizo speaker)
 

inglewoodpete

Senior Member
A 10k resistor between serial in and 0v is adequate.

The recommended capacitor between +5v and 0v is 0.1uF, mounted as close as practical to the power pins on the PICAXE/PIC chip.
 

120ThingsIn20Years

Senior Member
A 10k resistor between serial in and 0v is adequate.

The recommended capacitor between +5v and 0v is 0.1uF, mounted as close as practical to the power pins on the PICAXE/PIC chip.
Awesome... thanks

I forgot how quickly questions get answered on this forum. I was planning on checking late tomorrow :)
 

fernando_g

Senior Member
Even if you don't plan to re-program the devices, leave the preparation to do so.

One never knows, if in the future one one may need an update, an upgrade or some additional feature.
 

inglewoodpete

Senior Member
Even if you don't plan to re-program the devices, leave the preparation to do so.

One never knows, if in the future one one may need an update, an upgrade or some additional feature.
I agree. It is rare for me to exclude the programming socket in one form or another. As a minimum, I include both resistors but no socket - that way, I can clip a wire to the junction of the two resistors if I should need to reprogram the PICAXE. Note that 2 x SMD resistors is a possibility if space is an issue.
 

AllyCat

Senior Member
Hi,

+1 .

Or just put in one pull-down resistor of perhaps 100k on the Programming Input pin. The PICaxe should still boot fine, but you retain the option to program via a (required) external 22k, without attenuating the levels excessively.

Cheers, Alan.
 

westaust55

Moderator
I have also used the scheme to have just a 100 kOhm pull down resistor on the SerialIn pin.
You will need both the 22 kOhm and 10 kOhm resistors externally configured as per the PICAXE manual.
An AXE029 circuit can be constructed as a separate programming circuit.

Just having a 22 kOhm externally will result in a potential divider that will highly likely not work.
 

120ThingsIn20Years

Senior Member
Thanks everyone, advice taken.

This little project has been an excellent experence for me. I cant remember if I've ever made anything that just worked the first time I plugged it in, but this one did. In the past I've been a little obsessed with fitting it all on as small a board as I can but this time didnt bother. That's probably also part of wanting to leave out the serial plug, but life is so much easier if you give yourself a little room :)
 

fernando_g

Senior Member
Another reason:
Sometimes one "discovers" a command or code trick which makes your software more efficient.

Even though the original software may be working just fine, I like to re-program and retest the unit.

If it works fine, one has acquired a little additional knowledge that may come handy later.
 

hippy

Senior Member
Having the programming adapter, or a means to fit one, is also handy for debugging, should it be found that a project isn't behaving as expected, differently to how it behaved on breadboard or during testing.

It can be used both to monitor what is going on and to download test programs to verify hardware connection and behaviour.

Without that one just has to reflect and guess why something is not working and that can be incredibly hard to do. The process of moving the PICAXE chip from programming to project board can quickly become tiresome and frustrating, especially when there is no way to tell if heading in the right direction or the opposite.

One of the worst real world scenarios is when something has worked for days, weeks or months and then suddenly stops working. That can be a nightmare to figure out.

And there's always Sod's Law; if you fit it or allow for it you won't need it but, if you don't, you will wish you had.
 

120ThingsIn20Years

Senior Member
These devices were attached to the cooling water outlet of immaculately restored Putt-Putt boats...

23565


to scream an alarm if the cooling water intake was blocked by weed or whatever, and although there were only a few lines of code, I took your advice and added the plug, although I think if anything went wrong with them it would have been from water damage.

There wasn't a lot to them.

Basically that box in the middle of these old wooden working boats (fishing and transport) holds a 70 year old motor, and it sucks in water as coolant, and expels it as warm water. If the expelled water temperature (thermistor, external on the copper pipe) got too hot, the picaxe screamed at you.

To calibrate them, you put one hand over the water intake, another on the water outlet pipe to wait for it to get overheated, then you use your third hand to turn the screw pot until it started screaming.

You let the cooling water flow again, and put super glue or silicone on the pot to fix it in place.

Don't try this with your alloy head car engine :)
 

Captain Haddock

Senior Member
I have a warning system on my boat (twin VP's) that involves a temp sensor on the outside of the raw water pump, they get very hot very quick if the water supply isn't there, I did it because one was a sod for not priming on first startup after standing for a few weeks.
Mine was done with thermocouples using a circuit and prog 'borrowed' (Matherp I think, it was a good while ago) from here and displays the temps of both raw pumps and both stern glands (they had an issue too) as well as engine bay ambient temp on a glcd display at the helm, it would look well out of place on that boat of yours though, that's a very pretty looking tub.
ds18b20's work well too and you can have a string of them on one input if you check all the serial numbers first.
 

120ThingsIn20Years

Senior Member
I have a warning system on my boat (twin VP's) that involves a temp sensor on the outside of the raw water pump, they get very hot very quick if the water supply isn't there, I did it because one was a sod for not priming on first startup after standing for a few weeks.
Mine was done with thermocouples using a circuit and prog 'borrowed' (Matherp I think, it was a good while ago) from here and displays the temps of both raw pumps and both stern glands (they had an issue too) as well as engine bay ambient temp on a glcd display at the helm, it would look well out of place on that boat of yours though, that's a very pretty looking tub.
ds18b20's work well too and you can have a string of them on one input if you check all the serial numbers first.
Sadly that boat isn't mine.

Somehow I could never find the thousands of hours to restore one, or all the dollars :)

And yeah, some of the boat club members insist on running/risking losing their foot on a flywheel to start their motors. Putting an LCD even close to their boats would bring tears. Even the screamer I made would be frowned upon on one of the bare wood restored boats, but the painted ones that were being used regularly and being left out in the sun are a different story. The people with the classic style restoration just put their hand into the exhaust water every few minutes.

They do the screaming themselves when their boats overheat :)

I wish I could find the program I made. The siren was the main component of it (obviously ie read thermistor, adjust pot, scream if too hot) but I made this awesomely irritating sound that harmonised with itself as it waxed and waned in volume and pitch, and was the most annoying sound I could come up with :)

It's on a long dead linux partition on a long dead computer.

It was definitely the most useful thing I've made to date though, in spite of it being only a few lines of code (and another few hundred for the scream).
 
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