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In the schematics for the $50 robot I noticed that the LED is connected to the VCC pin (with it's + pin) of the ATMega8 without a resistor inbetween, so:VCC pin -> LED -> ResistorInstead of:VCC pin -> Resistor -> LED
Concerning the UART module, I've taken a basic MAX232 circuit with some capacitors and wish to add a status LED for both Tx and Rx which are supposed to light up when the module is transmitting or receiving. My initial idea was to place a small resistor and a LED on both the line between the Tx -> T1IN and Rx -> R1OUT. My concern here however is that adding extra components in the path of the TTL signal might mess up the voltage levels up.An other suggestion I based of the shifter RS-232 adapter (from SparkFun) which would involve placing a resistor and a LED between the power bus VCC and the Tx -> T1IN line and another one between VCC and the Rx -> R1OUT line:VCC -> resistor -> LED -> Rx or Tx lineI've added an image with the max232 circuit displayed twice. In both circuits I've highlighted the places where I would have the lines placed (and in circuit two I've crudely also painted the lines to VCC).Could anybody tell me wether one of these circuits would work or have an alternate solution to add status LEDs?
if the transistors are connected directly to the signal line TX & RX. instead of through resistors. Would this design work? is there some problem that will occur with out the resistors?
interesting.. I thought that the larger capacitance will filter out high frequency changes in voltage. so if the baud rate is high, the information will be distorted due to the capacitor resisting fast changes in voltage. and since the voltage is equal in an ideal wire. the info being transmitted and received will be destroyed?
Also the 100 k resistor is a pull down resistor right?
if the tx and rx lines are connected as shown with the pull down resistor, but the wire connecting the tx and rx to the transistors does not have any capacitor or resistor, would this be a problem?
doesn't the transistor have high input impedance? so that it will not load the TX and RX lines.
In this case i know that a static one will keep the LED on which is not good but other than that is there any adverse impact?
I know that the reactance of a cap is 1/wjC and that is a property of how current limiting the cap is in AC. but I also know that capacitors resist change in voltage by channeling current through them.
[...] if mosfets are used instead of transistors. would any of the resistors still be needed?