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Member Since: July 6, 2009

Country: United States

  • Certainly there must be a maximum current and maximum voltage rating for these. Does it really need to be “left as an exercise to the reader” to determine the maximum limits?

  • It would be nice the have a photograph of the screen in operation to see what it actually looks like (brightness, hue, gap between pixels, etc.). I generally would not buy a graphic display without at least some photos to consider.

  • It uses the transmitted signal input from the PC on the DE-9 connector ("RS-In" signal on the schematic) to charge a 10 uF capacitor (C1) through a diode (D1). The way it is connected, the capacitor will be charged produce a negative voltage with respect to ground. This voltage is made visible on the DE-9 transmit line ("RS-Out") through a weak (10 K ohm) pull up resistor. The PNP transistor in U1 (the transistor with its base connected to the TTL side RX-I line) overwhelms the weak pull up when RX-I is low, pulling the RS-Out line up to Vcc (+5 V, +3.3 V, or whatever the TTL side device provides).<br />
    <br />
    Therefore the "RS-232" outputs will range from, for a mark (1) bit, approximately 0.7 V above the negative voltage provided by the PC's output signal (0.7 V drop due to the diode forward voltage drop); and for a space (0) bit, the signal will be Vcc (5 V, 3.3 V, or whatever).<br />
    <br />
    I wonder if this will work reliably for 2.8 V target since RS-232 specifies that -3 V to +3 V is an invalid signal level.<br />
    <br />
    It's a clever little hack that uses so few components... kind of cool but perhaps not as reliable as a "proper" RS-232 level shifter?

  • Apparently inductor L1 in the schematic (220 uH) is underrated for the current passing through it. See the forum thread at http://forum.sparkfun.com/viewtopic.php?f=15&t=15448 where user "dstahlke" replaced the inductor with one rated for 500 mA and this caused the backlight to work better and also to draw one fifth the current it did previously!
    SparkFun, are you going to upgrade the inductor so we don't have to hack it ourselves?

  • Does this have .100 inch pitch connectors?

  • Will this work on the Arduino Pro board?

No public wish lists :(