The chip - this pin connects all the free-wheel diode cathodes so that they can suppress Thirdly you must connect pin 9 to the motor positive supply or you'll risk destroying ![]() You can limit current to each motor with a resistor in its own circuit, or collectively withĪ common resistor between the motor supply and all the motors. That's bad, ground is the reference, always connect grounds together without resistance. Secondly you propose adding a resistor to limit current to the GND pin of the ULN2003. Remember which device you're using, pretty much any darlington driver will be ![]() (However you can always use 1k resistors if you like - then you don't have to The ULN2003 has 2.7k input resistors built-in. Silly question but I am assuming the base current only matters when the pin is being switched ? ie: there is no need to worry about it when the outputs from the Arduino are low ? You take the desired current flow through the transistor and divide by the Beta to get the minimum Base current you need to provide ? If it is always the same then you are saying that as long as the calculated minimum base current is less than 20mA I can use a 200 Ohm resistor on the input side ? (since as you say - the calculation you provided gives the minimum Base current and anything higher is ok) Is the voltage drop across the diode always 1V or is that variable according to the desired current flow as well. I'm not sure I understand the second part of your explanation fully. I only have 0.00677864 BTC in total (haha) but you deserve a few fractions of a bitcoin for that ! That explains more to me in a few sentences than all the information I've tried hunting down all over the Internet. Thank you for the really clear explanation. Just not the order of calculations I need to do. I include a diagram to summarise my thinking and from where I am starting. I am completely new to electronics and my knowledge is limited to Ohms law but I think my confusion is compounded by not knowing fully how the current used by the Darlington effects the current in the input circuit.Ĭan anyone help me adopt a methodical approach to sorting out the calculations I need to do or to correct any wrong concepts I might have. You can maybe see my thinking is going round in circles. If so, I know I can calculate the current from Ohms law in the circuit being switched but I'm perplexed how I can determine the required input current from this and even if I could will it exceed the safe 20mA the Arduino prefers and therefore conflict with the decision to limit the current to that amount. Is this true ? Do I need to base the calculation of the input switching current to the Darlington on the current in the circuit that is being switched ? and therefore I need to know the relationship between the current in the switched circuit to the current in the switching circuit so I can choose a resistor that does not limit or exceed the input current to below or above (respectively) that required to switch the Darlington. I was told that the input current required by the Darlington depends on the current in the circuit being switched (I had thought it was independent). ![]() this doesn't take account of the current already being used by the Darlington Array. ie: all else being equal add a resistor to bring down the current from the supplied 40mA. To protect the Arduino I should limit the current in the circuit to 20 mA. The 5V outputs on the Arduino side is compatible with the Darlington inputs but I'm confused as to how I determine the resistance I need in the circuit owing to the competing needs of the Arduino and Darlington. My understanding (misunderstanding) so far. I know I could use relays or individual transistors to do the job and which in many ways might be more straightforward but the all in one size and cost of a Darlington appeals to me and I think once I have the calculations sussed it may prove to be an invaluable resource for this and any future projects so whatever arguments there may be against it's use (I keep an open mind) I would still like to understand the procedure. I'm hoping someone can explain in the simplest way possible the calculations I need to do for BOTH the circuits involved (The Arduino side of the Darlington and the circuit being switched side) to make sure I neither damage the Arduino or the Darlington array by the current and voltage I use for the motors (or any other component) in the circuit being switched. I am trying to get my head around how to use an Arduino Uno R3 with a Darlington Array 2003A to drive a series of small electric hobby motors.
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