Timeline for Maintaining pull down on a relay with a shift register
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Feb 19, 2016 at 18:49 | comment | added | CharlieHanson | That is watch 'latching' means. | |
| Feb 19, 2016 at 15:41 | vote | accept | Inc1982 | ||
| Feb 19, 2016 at 15:40 | comment | added | Inc1982 | Ahh thank you that clarifies it for me. From: allaboutcircuits.com/textbook/digital/chpt-12/… "The purpose of the output register is to maintain a constant data output while new data is being shifted into the upper shift register section. This is necessary if the outputs drive relays, valves, motors, solenoids, horns, or buzzers." I didn't realize that after it latches it is able to keep in an output register the voltage differentials on each pin that you were describing. | |
| Feb 19, 2016 at 8:48 | comment | added | CharlieHanson | 'High' and 'Low' signals have nothing to do with current; they refer to voltage. There is negligible current flowing between the Arduino and a shift register, at any time. The shift register provides the power to the devices it controls. | |
| Feb 19, 2016 at 7:26 | comment | added | Inc1982 | Thank you so much for the response. There's one small but important piece of information I'm missing. In my understanding a HIGH signal is say 40ma on an arduino pin, while a LOW signal is 0ma. In-between latches, is the signal kept constant until it is switched again? If so, that would imply that there is some constant power coming from the Arduino that is being fed through the shift register and out the pins. This must be separate from the 8 bits being pushing into the Arduino. Is that why shift registers need a separate power supply? | |
| Feb 17, 2016 at 17:26 | comment | added | CharlieHanson | @Inc1982 I've edited the answer, I hope this helps. | |
| Feb 17, 2016 at 17:25 | history | edited | CharlieHanson | CC BY-SA 3.0 |
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| Feb 17, 2016 at 14:48 | comment | added | Inc1982 | Thank you for your response. Indeed, I do have a misunderstanding. There's one thing I'm still missing. If a relay requires a constant voltage, and the latch triggers every 8 clock cycles. How is a 'HIGH' signal maintained when using the shift register. Another way of putting it: if I have some code that runs on a scheduler every 1 second, and that code shifts all HIGH values into the register and latches it so it pushes a HIGH signal out, will the value drop to LOW between my 1 second intervals when I'm not actively pushing data.. if it does not shift to LOW, why is the HIGH value maintained? | |
| Feb 16, 2016 at 9:12 | comment | added | Ignacio Vazquez-Abrams | Not all shift registers have latching. | |
| Feb 16, 2016 at 8:54 | history | answered | CharlieHanson | CC BY-SA 3.0 |