PICAXE 08M2 - basic connections handouts

#1
Hello everybody,
I help my friends to know PICAXE and I got an idea to make a serie of handouts with basic connections for 08M2. Maybe it comes handy for everybody else. I will add more of them in this thread, but the progress will be slow depending on my free time. Here is the first one. I hope not to break any rule with this activity.

EDIT: some sentences fixed
 

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#2
Item #1 seems contradictory. R1 (or similar) at least needs to be in all circuits, connecting C.5 to 0V if R2 is absent. Better always to include both resistors, and I personally also always include the 2-pin programming connector.

Re item #3, I believe the maximum voltage is 5.5 volts. You might put in that the most convenient way to power the picaxe (and perhaps safest if something is wrong with your circuit) is with 2-AA or 3-AA batteries.
 
#3
Item #1 seems contradictory. R1 (or similar) at least needs to be in all circuits, connecting C.5 to 0V if R2 is absent. Better always to include both resistors, and I personally also always include the 2-pin programming connector.

Re item #3, I believe the maximum voltage is 5.5 volts. You might put in that the most convenient way to power the picaxe (and perhaps safest if something is wrong with your circuit) is with 2-AA or 3-AA batteries.
Thank you for your comments. Because it is intended for complete beginners I prefer "better safe than sorry". I would like to know what you think about it. If it is worth to note down much more details and explanations - I do not want the beginners to be confused and overloaded with information. Thank you for every comment and ideas. I added note about batteries.
 
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#4
This sentence should be reworded:
Do not leave the plug J1 and the resistors R1, R2 in all your projects (the resistors R1 and R2 makes the circuit to operate reliably).
I would suggest something like what is stated in Manual 1:
Always use the 10k/22k resistors (R1 & R2 as shown above), even if the chip was programmed on a different board.
 
#7
Two comments on your second circuit in post #6.
  1. You have probably excluded the programming resistors (R1, R2) for simplicity but I suggest you include a note saying that they must be included in a working model.
  2. Depending on the forward voltage drop of D3 and D4, you may not be able to able to turn both LEDs off. I assume you mean that the LEDs can be turned off by making the PICAXE pin an input. If the LEDs have a forward voltage drop of 1.8 to 2.1 volts, then they will conduct and light up with current flowing from Vdd-R6-D4-D3-R5-Gnd.
 

Pongo

Senior Member
#8
Regarding the second circuit in post #6.

I think your #3 led configuration is not a reliable design for a couple of reasons, the #4 configuration is OK.

Modern LED's can be well into conduction with less than 2 volts applied, often around 1.75 volts. In #3 it's not guaranteed that C.4 will always be hard high or low, especially during start up. If C.4 is high impedance, with 5 volts Vcc and no series resistance, you can have a significant current flowing through the two LED's, I = ((5 - 3.5)/a very small resistance) which is not good for the diodes.

Also there's also no guarantee that the "off" LED will really be "off". Suppose C.4 is high, D3 will be lit, and let's suppose the voltage across it is 2.2 volts. This means the Anode of D3 and Cathode of D4 will be at + 2.2 volts. The voltage across D4 will be 5 - 2.2 = 2.8 volts.

The #4 configuration where the picaxe is basically shorting out the unlit LED and there is always series resistance in circuit avoids both problems.

One other point, don't send your audience on a hunt for hard to find parts. 230 ohms is not a commonly available resistor value. I'm not sure what resistor ranges the average hobbyist has access to. I guess the 10% tolerance E12 range is pretty common and it goes 220, 270, 330, I stock the 5% E24 range, that series has 220, 240, 270. Try to always suggest a suitable standard value substitute for calculated values.
 
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