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  • playinmyblues commented on mrmath's instructable Using a shift register with Raspberry Pi10 months ago
    Using a shift register with Raspberry Pi

    A couple of words of caution:1) In Step 2), it looks like you are using one current limiting resistor and is it 22 ohms? 1/4W or 1/2W? Using one current limiting resistor with 8 LED's will make all the current go through one resistor. That can be bad for a project.Say Vled = 1.8VVpin = 5VVresistor = Vpin - Vled = 5V - 1.8V = 3.2VR = Vresistor / IsinkIf I read the spec sheet correctly for a TI SN74HC164, I(input clamp) = +/- 20mAI think that is the maximum current that can be sunk by a pin when low.R = 3.2V / 20mA = 16 ohmsHowever, you have all LED's routed through one resistor.I = 3.2V / 22 ohms = 0.145A0.145A x 8 = 1.16AP = (I^2)R = (1.16A ^ 2)22ohms = 29.6WIf you have your project working with these values, I must have missed something - it would not be the 1st time!1.16A would be far...

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    A couple of words of caution:1) In Step 2), it looks like you are using one current limiting resistor and is it 22 ohms? 1/4W or 1/2W? Using one current limiting resistor with 8 LED's will make all the current go through one resistor. That can be bad for a project.Say Vled = 1.8VVpin = 5VVresistor = Vpin - Vled = 5V - 1.8V = 3.2VR = Vresistor / IsinkIf I read the spec sheet correctly for a TI SN74HC164, I(input clamp) = +/- 20mAI think that is the maximum current that can be sunk by a pin when low.R = 3.2V / 20mA = 16 ohmsHowever, you have all LED's routed through one resistor.I = 3.2V / 22 ohms = 0.145A0.145A x 8 = 1.16AP = (I^2)R = (1.16A ^ 2)22ohms = 29.6WIf you have your project working with these values, I must have missed something - it would not be the 1st time!1.16A would be far too high for even a 1/2W resistor.2) A schematic would go a long way to resolving what is going on here, what the resistor value is, exactly how the IC, LED's and resistor are all connected.3) A list of components or BOM would also make things easier, especially when trying to gather your parts. This might seem unecessary with a project with only three different electronic components invovled, but it would resolve my questions.

    I could not open any of the videos you provided.

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  • Build a Square Wave Oscillator - Part 1 of DIY Modular Synths

    Try looking up 4 op amp function generator. That should give you enough to figure out how to get a pseudo-sine and triangle waves.

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