555 Timer

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555 Timer

This topic has 10 replies, 8 voices, and was last updated 28 July 2015 at 11:59 by Les Jones 1.

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27 July 2015 at 13:15 #198105
JA
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@ja
I have started to think about designing and making a tachometer for use on a milling machine and/or model IC engine. Looking at various designs some use 555 timers.

Like a lot of others I have used 555 timers and know that they are either loved or hated. I would like to know the reasons.

JA
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27 July 2015 at 13:15 #31797
JA
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@ja
27 July 2015 at 14:25 #198112
Neil Wyatt
Moderator
@neilwyatt
The 555 – electronic Duck Tape.

Loved, because it is one of the most ingenious chips of all time, and the various components on board make it a useful toolkit for experimenters and inventors.

Hated, because you can do everything it does more cheaply, with less currenet and vastly more flexibility with a small microcontroller and fewer components.

Of course, you don't need to program a 555…

Neil

(some may also mention that there are now more accurate, lower current versions of the 555 available)
27 July 2015 at 14:46 #198114
Les Jones 1
Participant
@lesjones1
Hi JA,
You need to specify how you plan to use the 555. If you plan to use it as the monostable in a frequency to voltage converter with an analogue meter for the display then they are OK. If you plan to use it generate the gate time to count pulses and display them on a counter made from CMOS or TTL ICs (Or a microcontroller.) then they are a poor choice. Using them in either of the above ways you would need to calibrate the tachometer. If you use a microcontroller which probably would use a crystal clock (Some have an internal oscillator which would be accurate enough for displaying the speed of a lathe or milling machine. ) there will be no need to calibrate it.

Les.
27 July 2015 at 15:07 #198115
Nick_G
Participant
@nick_g
.

I have used one of these. **LINK**

Power supply from an old mobile phone charger, popped in a case and "Bobs your uncle"

Nick
27 July 2015 at 15:08 #198116
john swift 1
Participant
@johnswift1
have you looked at Philips application sheet AN170 ?

**LINK** see page 10

one problem with the original "555" is the large current pulse it takes from the supply as the output pin 3 switches

( for an instant the output stage short circuits the supply !!!)

very often I use the low current 7555 cmos version

john

ps

diy 555

**LINK**

pps

the CSS555C a programmable "555"

http://www.customsiliconsolutions.com/downloads/Revised%20Standard%20products/CSS555C_Spec.pdf

Edited By john swift 1 on 27/07/2015 15:15:54
27 July 2015 at 15:24 #198117
Keith Long
Participant
@keithlong89920
Unless you really want to build a unit, there are plenty of folk on E-Bay selling contactless tachos that go up to 99,999 rpm as well as covering milling machine speeds for less that £10 delivered. I've got one, works just fine, as a quick claibration check I just point it at a standard flouresccent tube to get a reading of 6krpm.
27 July 2015 at 16:44 #198123
wheeltapper
Participant
@wheeltapper
Posted by Nick_G on 27/07/2015 15:07:00:

.

I have used one of these. **LINK**

Power supply from an old mobile phone charger, popped in a case and "Bobs your uncle"

Nick

+1 on these, simples. an old computer power supply.

Roy

Edited By wheeltapper on 27/07/2015 16:44:55
27 July 2015 at 18:42 #198133
Muzzer
Participant
@muzzer
I looked at this fairly recently and although you can buy a simple tacho off ebay for pennies, I rather liked the machtach device. This can be set up for a variety of different pulses per rev, so you could trigger off a reflective sticker or a gear and it supports a variety of inputs including IR reflective, Hall and VR sensors.

To me, the most appealing feature was the ability to specify a cutter / workpiece diameter and then display the surface speed in feet or metres per minutes. This works for both lathes and milling (and drilling) machines. I bought the kit and built it up without any problem, although you can buy it ready made if you prefer. Nicely developed and very flexible. The postage was actually cheaper than advertised and the guy refunded the difference. I have a second kit to build up for the lathe when I get a round tuit.

Simple and easy to use – recommended. More pics in my album.

Murray
28 July 2015 at 11:27 #198219
JA
Participant
@ja
Many thanks for the replies.

I intend to design and build a couple of tachometers over the winter when the cold drives me from the workshop. This is more to keep my brain occupied and fingers nimble rather than to save money.

I have looked at a number of designs from the simple, using a monostable 555 timer, to the quite sophisticated. I consider the Mach-Tach instrument the bench mark and could be tempted to buy a couple of kits or just their chips. I have also noted the LM2907 frequency to voltage converter which is readily available.

JA
28 July 2015 at 11:59 #198222
Les Jones 1
Participant
@lesjones1
Hi JA,
There is a tachometer design on my website that may be of interest to you. It was designed a few years ago and the hall effect gear sensor I suggested is no longer available but there a probably a number of alternatives.

Les
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