Timeline for Why doesn't my 555 + MOSFET setup drive my motor?
Current License: CC BY-SA 3.0
22 events
| when toggle format | what | by | license | comment | |
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| Jul 2, 2017 at 15:20 | vote | accept | CaptainCodeman | ||
| Jul 2, 2017 at 7:38 | comment | added | Russell McMahon♦ | As well as cap for the motor feed (you mention 1000 uF) add a small series resistor in the feed between the cap and the motor that drops say 0.25V. (eg if motor current = 100 mA then R = V/I = 0.25/0.1 =~~ 2.5 Ohms. The R & C form a filter which helps isolate the motor noise. | |
| Jul 2, 2017 at 6:40 | comment | added | CaptainCodeman | OK I think I figured it out, the pull-up resistor goes between pin 2 and the +9, right? I added it and it all seems to be working smoothly now. | |
| Jul 2, 2017 at 6:20 | comment | added | CaptainCodeman | (By the way I can't use a 9V battery; it's too heavy to fly. I have an 8v LiPo battery on the drone and an extra 3.7v LiPo to power the motor.) | |
| Jul 2, 2017 at 6:19 | comment | added | CaptainCodeman | OK thank you so much for your suggestions. I attached a 1000uF capacitor in parallel to the motor and it seems to be working most of the time now. I also attached the 10nF capacitor to pin 5. Where do I connect the pull-up resistor? | |
| Jul 2, 2017 at 6:01 | comment | added | markshancock | Other possibility is pin 2. When switch is off, there is nothing to pull that input solid high. I recommend a pull-up on that line (10K?). Could go lower to make more noise resistant | |
| Jul 2, 2017 at 5:58 | comment | added | markshancock | Try connecting the 555 and RC to a 9V battery. | |
| Jul 2, 2017 at 5:58 | comment | added | markshancock | Ceramic on pin 5. Ceramic on supply was to try to cut out noise from the motor. | |
| Jul 2, 2017 at 5:33 | comment | added | CaptainCodeman | @markshancock OK I attached a 2200uF electrolytic capacitor to in parallel to the 9v source, still the same problem. Is the ceramic capacitor the one that goes on 555 pin 5? How can I isolate the supply from the motor? | |
| Jul 2, 2017 at 5:20 | comment | added | markshancock | "simply attaching the motor to the 3v power, resets the timer on the 555" Ahhh. That is what is going on. That may be hard to debug with a DVM. A bit more complicated to explain i a comment. You probably need to isolate the supply (and RC) from the motor and add parallel electrolytic and ceramic capacitor. The noise from the motor is likely tripping the 555. Also you may need to make the input to pin 2 less noise sensitive. | |
| Jul 2, 2017 at 5:12 | comment | added | markshancock | @replete IRFZ34 already has an integral DS protection zener so flyback diode is not required. | |
| Jul 2, 2017 at 5:10 | comment | added | CaptainCodeman | Sorry I mean, when the negative poles of my 3v and 9v power supplies are connected, simply attaching the motor to the 3v power, resets the timer on the 555. I don't have info about the motor, I just ripped it out of a toy car that runs on 2 AA batteries. | |
| Jul 2, 2017 at 4:55 | comment | added | user133493 | The motor doesn't run consistently connected directly to your 3V power supply? What's your power supply? Got a motor datasheet, or information about its current requirement? | |
| Jul 2, 2017 at 4:48 | comment | added | CaptainCodeman | @replete I added a diode across the motor, still the same problem. Actually for some reason it happens even if I just attach the motor to the 3v power | |
| Jul 2, 2017 at 4:46 | comment | added | CaptainCodeman | @replete To reverse the signal. Otherwise the motor would turn on for 20 seconds and then turn off. | |
| Jul 2, 2017 at 4:46 | comment | added | user133493 | You should have a flyback diode across the motor to protect the switch. | |
| Jul 2, 2017 at 4:44 | comment | added | user133493 | Could you explain why you're driving the MOSFET with a BJT rather than directly from the 555 output pin? | |
| Jul 2, 2017 at 4:02 | answer | added | markshancock | timeline score: 2 | |
| Jul 2, 2017 at 3:52 | history | edited | CaptainCodeman | CC BY-SA 3.0 |
added 3 characters in body
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| Jul 2, 2017 at 3:46 | comment | added | user103380 | nMOS symbol is a similar symbol to a transistor, but it's more of a square shaped looking switch symbol (hard to explain but you can look it up on Google). | |
| Jul 2, 2017 at 3:43 | review | First posts | |||
| Jul 2, 2017 at 6:20 | |||||
| Jul 2, 2017 at 3:42 | history | asked | CaptainCodeman | CC BY-SA 3.0 |