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Chapter 9 Acitivity 1 Version 2.2 — Parallax Forums

Chapter 9 Acitivity 1 Version 2.2

Electrically ChallengedElectrically Challenged Posts: 22
edited 2012-05-31 03:18 in Learn with BlocklyProp
I having problems with the transistor in this section. Was there ever any issue with the layout for this or (assuming I haven't messed up the wiring - which I've redone 3 times) do I just have a bad transistor?

Can I test this like a relay? I attempted testing it earlier, but wasn't sure if I was doing it correctly.

Thanks,

EC

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-05-30 16:36
    Parallax publishes a lot of books.

    "Chapter 9 Acitivity 1 Version 2.2" of what? (A link would be nice.)

    What kind of transistor are you using.

    What did you expect to happen? What did happen to make you think something is wrong?
  • Electrically ChallengedElectrically Challenged Posts: 22
    edited 2012-05-30 17:12
    2N3904 is the transistor. There are two layouts for this - one with the dial potentiometer - increasing the brightness of an LED while turning the dial. The other is sending a pulse to an LED - one high, one low via code and Pin8. I didn't get light out of the LED in either instance - and I have tried different LEDs.

    Probably a moot point now since I went out and purchased several bags of transistors since I'd need them later for a robot of some kind.

    But can you test them like relays? My multimeter doesn't have a diode or transistor tester.

    Thanks,

    EC
  • Electrically ChallengedElectrically Challenged Posts: 22
    edited 2012-05-30 17:34
    Hmmm!! Still not working. This is the drawing from the book. I have it laid out just as in the drawing. I don't understand the two resistors, but...

    Fig 9-4.jpg
    Fig 9-4.jpg
    540 x 264 - 99K
  • Mike GreenMike Green Posts: 23,101
    edited 2012-05-30 19:47
    The two resistors are used because 100K is too high (doesn't provide enough current for the transistor's base) and the parts kit only has 100K resistors. Two in parallel make 50K. By Ohm's Law, with roughly 5V on the Stamp I/O pin, that's about 100uA into the base. A 2N3904 has a minimum gain of 40 at that current, so there'd be about 0.1mA x 40 = 4mA current flow through the LED, enough to cause it to light. If it's not working, either the transistor or the LED is wired wrong. Figure 9-4 is correct as far as the transistor's appearance is concerned. The flat area on the ring that sticks out of the base of the LED (where the leads come out) marks the cathode (with the bar on the schematic). The longer lead is the anode (with the triangle on the schematic).
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-05-30 20:37
    Electrically Challenged wrote: »
    I have it laid out just as in the drawing.

    I just want to make sure you carefully read Mike's description of the LED. The drawing makes it look like the short lead is connected to Vdd; the long lead (on the anode side) connects to Vdd not the short lead.

    The flat side of the LED Mike mentioned is sometimes a small "nib" of plastic. Whatever shape it may be, the side with an edge different than the rest of the LED is the cathode side (in this circuit the cathode connects with the transistor).
  • Electrically ChallengedElectrically Challenged Posts: 22
    edited 2012-05-31 03:18
    I wondered about that. I've been moving through the text at a brisk pace, so I missed that. I'll spin it around and try that. Yep, now it's blinking. Excellent.

    Thanks,

    EC
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