the "best" 555 timer and motor control? - Page 1
Forum section: electronics / beginners

author: MrZwing
author_rank: Regular Contributor
timestamp: April 07, 2017, 09:40:59 am
content: So I have a odd little question I have trying to take a deep dive into 555 timers and its cousins and there is a LOT of them.but what I am looking for is the most durable (even been looking at ceramic military grade stuff) and most precise of them all or at least close to the precise of them all. its probably overkill for my application but still I like having good stuff in my circuits.so anyone have any idea which ones I should look at since apparently I'm to good for the classic NE555. trying to make a high precision constant speed controller for DC motors. so if anyone has any ideas for that I would like that too if there is some even better way than PWM.

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2017, 12:19:32 pm
content: Quote from: MrZwing on April 07, 2017, 09:40:59 amIf you need precision, then don't use the 555 timer.Why would you need precision for PWM? It's generally not necessary?

author: MrZwing
author_rank: Regular Contributor
timestamp: April 07, 2017, 02:44:02 pm
content: What should I use for precision? since 555 isn't that good PWM is just the thing I know so would like to know what to look at instead?

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2017, 03:11:52 pm
content: Quote from: MrZwing on April 07, 2017, 02:44:02 pmA micro-controller with a crystal controlled clock?Still, a 555 is more than accurate enough for controlling the speed of a DC motor using PWM.

author: Seekonk
author_rank: Super Contributor
timestamp: April 07, 2017, 04:01:29 pm
content: The stability of the 555 depends on the stability of the power supply. This is why they are noted for doing glitchy things. Any of the switching regulator chips, TL496 etc,have a built in voltage reference and can do most of the same functions. You don't have precision unless you have feedback and a regulator chip would tie that in better.

author: ebastler
author_rank: Super Contributor
timestamp: April 07, 2017, 06:04:56 pm
content: Quote from: MrZwing on April 07, 2017, 09:40:59 amWhat level of "precision" are you aiming for?Driving a motor with PWM is essentially an "open loop" approach. I would expect that it is not the precision of the PWM duty cycle which limits how exact the motor speed can be kept constant, but rather changes in motor winding resistance (as a function of temperature) and mechanical resistance (as a function of mechanical load and bearing resistance). Hence, no point in trying to obtain an ultra-precise PWM ratio.Closed loop control would give you more precision: Measure the actual motor speed, using e.g. optical encoders or a hall effect sensor. Then adjust the PWM ratio to reach and maintain the desired target speed.But the first step should be to define what tolerance you can accept for average speed (long-term average and drift), and short-term speed fluctuations.

author: Ian.M
author_rank: Super Contributor
timestamp: April 07, 2017, 06:20:26 pm
content: Any CMOS 555, a 1% regulated supply to the 555, 1% timing caps and resistors, and a bipolar complementary emitter follower buffer stage on the 555 output powered off the unregulated supply so the output loading doesn't significantly heat the 555 or regulator dies and it will be as good as you'll ever get from a 555 style circuit. You can probably hold the output pulse to a few percent accuracy all-in.I remember a Commodore PET serial port board I modded many years ago for a higher baud rate, that used a bipolar 555 for the UART clock generator so you can certainly hold better than 5% or it would never have worked reliably.