Forum sponsored by:
Tachometer design
Views on tachometer design
| Steve Garnett | 31/01/2010 13:49:49 |
| 837 forum posts 27 photos | Yes, the Spanish page is certainly interesting. The only real snag (and it is a very real snag) is the line that says: "The program for the PIC is not available, anyone interested in construction can send the CIP schedule at an affordable price." Which seems to indicate that if you send him a PIC, he'll program it for you and send it back - at what he determines to be an affordable price. Or, you write your own code. And on a technical note, I'm not convinced that using a 741-type device (rather obsolete) in the tacho preconditioning circuit is exactly a brilliant idea, even though it's been used only as a threshold detector, but that doesn't really matter very much. But as you say, the features list is certainly interesting - well, a bit of it is. I like the idea of an approximate metres or feet per minute indication, but I'm not quite so sure what I'd ever use the rest of the facilities for. And if somebody could please enlighten me as to what the purpose/value of being able to send the speed data back to a PC is, I'd be quite intrigued. Edited By Steve Garnett on 31/01/2010 13:51:11 |
| John Rudd | 31/01/2010 15:59:00 |
| 1479 forum posts 1 photos | I too checked the website...Couldn't see any pic code so gave up..
Personally I'd have used an LM393 or similar comparator for the pre conditioning cct...As for the remeote read on a pc...Superfluous imho... |
| Stub Mandrel | 31/01/2010 21:01:11 |
 4318 forum posts 291 photos 1 articles | First: I'd like to see Les get his article published and then we can stand well back and see what happens! Most micros these days have bult in comparators that will do the job as well as or better than an LM393, though a sensor (opto or hall effect) with built in conditioning is the most reliable solution. Many micros have serial ports that can easily speak to a PC, just add a MAX232 or similar to get the right levels, or even a USB-RS232 convertor to allow USB connection. The problem with a PC link is getting the PC to do something with the data. Can I plug BBC Basic for Windows by from Richard Russell - the best £30 i ever spent on computing related stuff. If you used to play with home computers years ago, then this will allow you to do all your old tricks and use windows interfaces without the pain and anguish of Visual BASIC or similar. Neil |
| John Rudd | 31/01/2010 22:45:00 |
| 1479 forum posts 1 photos | Posted by Neil on 31/01/2010 21:01:11:
Most micros these days have bult in comparators that will do the job as well as or better than an LM393,
Neil
Sure, the 16F628A has a couple of compartors built in...but iunless you know how to use/disable them they are not much value to those that wield a turning tool...
Guys...Lets not get hung up on the why/wherefore etc of this project, just accept that someone has come forward with a worthwhile project....If electronics isnt your bag then dont criticise the OP for his offering..
For those that have experience, let's not criticise Les for his efforts to make life simple...
Edited By John Rudd on 31/01/2010 22:46:55 |
| Roy | 01/02/2010 07:56:33 |
 13 forum posts | John,
I echo your thoughts, Thanks Les for the offer of a low cost, easy to assemble and functional Tacho.
For those of us into Electronics Design, we can either accept the project as is or if you feel you can improve then do so.
As for choice of micro, using the onboard comparitor is not difficult but will add overhead in code and time to execute instructions.
|
| Gerald Weare | 01/02/2010 08:29:35 |
| 9 forum posts 7 photos | As one who has built a number of very successful tachos using the 16F628, the comparators are neither here nor there. You need to have a digital filter in any case, so the hysteresis of the regular Schmitt trigger digital ports is fine. In any event, I don't believe the comparators have any hysteresis? Been a while since I looked at them. Plus you probably need pull-ups for the comparators. My tachos work just as well on a 16F84 as the '628. All you need of the PIC is one input and enough output bits for the display. What does seem to help a lot is to have an IR detector (or gear tooth sensor if that's what you like) with a built-in Schmitt trigger. Saves a chip. I use nothing but the PIC standard I/O port and the sensor.
BTW, I can recommend the use of the FED (Forest Electronic Development) PIC C compiler package. It is full featured, including assembler, libraries for all the PIC subsystems, for driving LED and LCD displays and other devices, development environment, simulator, etc.. Very reasonably priced too, and good support. Of course Microchip also has their free MPLAB environment which is fine, but last time I looked they were charging for the C compiler.
They also have an AVR product, but I have never used that chip. |
| Steve Garnett | 01/02/2010 10:43:55 |
| 837 forum posts 27 photos | Posted by John Rudd on 31/01/2010 22:45:00: For those that have experience, let's not criticise Les for his efforts to make life simple... John, I wasn't aware that anybody was criticising Les at all - exactly the opposite, in fact. |
| Les Jones 1 | 01/02/2010 15:49:08 |
| 2292 forum posts 159 photos | Hi all, This reply is to Hugh Gilhespie's of Jan 31st I think your offer is very kind as it would bring down the cost. I did a costing of parts from Farnell and Rapid. Farnell worked out to £8.23 and Rapid £5.87 including VAT This is on the assumption that resistors could be bought in units of one. Farnell minimum is 50, Rapids is 100. For someone buying the parts for one unit (From Rapid ) they would have to buy 680 resistors more than required which is £3.40 + VAT which is £4.00 They would then have to Pay postage which is £4.95 (On orders under £30.00) The total cost for one would come to £14.82 which would make it too expensive. This does not cover the cost of stripboard and bits of wire or a PCB A problem you would have is having some idea of the numbers involved. If the numbers were high then a manufactured PCB would be the best solution. I have tried to do a PCB layout with "Eagle" software but I have not yet mastered it properly. I would be happy to program the PIC's If you want a copy of the costing spreadsheet send me a message on this forums messaging system with an email address so I can send you a copy. (I would not advise putting a email address in this part of the forum as it may result is you receiving spam.) Les. |
| Les Jones 1 | 01/02/2010 16:02:20 |
| 2292 forum posts 159 photos | Hi Neil, There is no reason why an internal analogue comparator should not be used. It would require a PIC with three more I/O pins as I can see no way in firmware of internally routing the output of the comparator to the CCP input so it would have to be hard wired between the comparator output and the CCP input. I do not think this would improve the performance in any way but it may save some space. Removing an 8 pin IC but requiring going from an 18 pin PIC to a 28 pin one. I am making the source code available as well as the hex code so anyone can modify it to suit their requirements. (Or decide after looking at the code they do not like the design and go to another design.) Les. |
| Stub Mandrel | 01/02/2010 22:06:25 |
4318 forum posts 291 photos 1 articles | Thanks Les, Glad you took my post in the spirit intended. I'm not familiar with PICs and their architecture, but I can apprecaite the pin issue - driving displays eats output pins! Why not look at hall effect switches? They contain a schmitt trigger and all conditionng circuitry, all you need is a +3 to +30v supply, and a pull up to Vdd on the output: http://uk.farnell.com/allegro-microsystems/a1104eua-t/hall-effect-switch-sip-3/dp/1521705 I find one of these 100% reliable. Neil |
| Les Jones 1 | 02/02/2010 09:20:43 |
| 2292 forum posts 159 photos | Hi Neil, If you look back through this thread you will see that I suggested using hall effect gear sensor in the situation where sensing teeth on an existing gear on the machine is the simplest option. These have the magnet built in and automatic threshold adjustment so that the gear to sensor distance is not critical. There are two types of these. The two wire type requires a sense resistor in series with it (About 100 ohm is suitable.) The three wire type which would be ideal as it could be connected directly to the PIC carries a one off import charge of £15.95 which makes them too expensive to buy in one off's. The part number of the two wire type is ATS642LSHTN (Farnell code 1521698) I used a device similar to the one you suggest with an external small magnet on my mill and that works well. For situations were there is no existing gear to sense then a reflective optical sensor is easy to install fitting it close to a rotating part with a reflective marker stuck to it. Both the two wire gear sensor and the optical sensor require an adjustable threshold. The design is aimed at non electronics people so I wanted it to be simple to use with either sensor. (If the unit was limited to using the exact hall device I suggest then the threshold could be set to a calculated value with fixes resistors.) Les. |
| Stub Mandrel | 06/02/2010 22:06:08 |
4318 forum posts 291 photos 1 articles | Fair point on the gear sensors, but I wanted something that made one pulse per rotation, as I was timing one pules, rather than counting pulses in a tiome period. Same view, but looking down the other end of the telescope! To be honest, I think half the reward of designing something like this is trying the various options - if they weren't valid options then we wouldn't have so many parts to choose from. I think my bias for a magnetic sensor has more to do with the elevated oil and dirt levels around my lathe - I'm not sure a reflective marker would remain refelctive too long with me around  When you do your article you could consider giving examples of different sensor types and their pros and cons. Neil |
| harold | 23/02/2010 17:40:06 |
| 35 forum posts | Just noticed Les has updated his website with Tach Rev3a. On behalf of those like me, who are enthusiastic but ignorant: Thanks! H |
| Les Jones 1 | 23/02/2010 18:16:06 |
| 2292 forum posts 159 photos | Hi Harold, Most of the changes on the website are as a result of things I find that need to be done before the information is in a form that can be submitted for publication. It is also a result of me trying to fully understand how to manipulate files on the website. At first I just used Microsoft Frontpage Publish function to create the website without really understanding what it was doing. The 3a version software is a result of me noticing I had not put leading zero blanking on it. This has now been added. Also in the parts list the Kingbright display has been removed as the pin layout is slightly different to the Avego display I had used originally. Les. |
| Dave Tointon | 01/03/2010 11:00:12 |
| 49 forum posts | G'Day Les,
I know next to nothing about electronics, despite using complex electronic equipment every day. ie coffee machine, toaster, car, mobile telephone etc etc. I feel that an article in MEW for a tachometer would be an ideal way for us older blokes to learn something about this black art!!!! Especially if you could explain what some of those little components like resistors, transistors, chips etc actually do. I'd love to build one, please David
Regards
Dave Tointon. |
| Rogeman | 03/03/2010 15:04:50 |
| 6 forum posts 1 photos | I have followed this thread with interest and hope to learn to programme a Pic well enough to make my own Tacho one day.
Having searched the web this looks to be a good system and its free
Regards
Roger
Edited By Katy Purvis on 01/06/2015 12:20:25 |
| Les Jones 1 | 03/03/2010 15:54:21 |
| 2292 forum posts 159 photos | Hi David, The article (If accepted.) is only intended to give enough information to enable someone with little or no electronics knowledge to build and install the tachometer on a lathe or mill. MEW would not be the place to teach basic electronics and PIC programming. The source code will also be available on a website for those that are interested in understanding how it works. (Or for people to modify to suit their own special requirements.) One of the electronics magazines would be the best place to start to learn electronics. Les. |
| David Clark 1 | 03/03/2010 16:00:20 |
 3357 forum posts 112 photos 10 articles | Hi Les
I have no intention of doing basic electronics in MEW.
Everyday and Practical Electronics is the place for that.
regards David |
| Les Jones 1 | 03/03/2010 16:17:38 |
| 2292 forum posts 159 photos | Hi David, (David Clark) My last post was a reply to Dave Tointon's post. ( I made an error writing David instead of Dave.) Sorry if it caused any confusion. Les. |
| Dave Tointon | 03/03/2010 23:49:04 |
| 49 forum posts | G'Day Les and David,
Fair enough, I'll just have to learn the basics from somewhere else, but still very keen on an article please. This website is something of a trap. In the last week , through various links, I have found enough workshop projects to keep me busy for months. All stuff that I cannot live with out of course. My wife is a bit cross with you David!!!!! but I am very happy with your good work.
Regards
Dave Tointon |
Please login to post a reply.
Magazine Locator
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
Sign up to our Newsletter
Sign up to our newsletter and get a free digital issue.
You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy
Latest Forum Posts
- hemingway ball turner
04/07/2025 14:40:26 - *Oct 2023: FORUM MIGRATION TIMELINE*
05/10/2023 07:57:11 - Making ER11 collet chuck
05/10/2023 07:56:24 - What did you do today? 2023
05/10/2023 07:25:01 - Orrery
05/10/2023 06:00:41 - Wera hand-tools
05/10/2023 05:47:07 - New member
05/10/2023 04:40:11 - Problems with external pot on at1 vfd
05/10/2023 00:06:32 - Drain plug
04/10/2023 23:36:17 - digi phase converter for 10 machines.....
04/10/2023 23:13:48 - More Latest Posts...
- View All Topics
Support Our Partners
Shopping Partners
Subscription Offer
Latest "For Sale" Ads
- Reeves** - Rebuilt Royal Scot by Martin Evans
by John Broughton
£300.00 - BRITANNIA 5" GAUGE James Perrier
by Jon Seabright 1
£2,500.00 - Drill Grinder - for restoration
by Nigel Graham 2
£0.00 - WARCO WM18 MILLING MACHINE
by Alex Chudley
£1,200.00 - MYFORD SUPER 7 LATHE
by Alex Chudley
£2,000.00 - More "For Sale" Ads...
Latest "Wanted" Ads
- D1-3 backplate
by Michael Horley
Price Not Specified - fixed steady for a Colchester bantam mark1 800
by George Jervis
Price Not Specified - lbsc pansy
by JACK SIDEBOTHAM
Price Not Specified - Pratt Burnerd multifit chuck key.
by Tim Riome
Price Not Specified - BANDSAW BLADE WELDER
by HUGH
Price Not Specified - More "Wanted" Ads...
Get In Touch!
Do you want to contact the Model Engineer and Model Engineers' Workshop team?
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.
Digital Back Issues
Donate
Register
Log-in
Model Engineer Magazine
- Percival Marshall
- M.E. History
- LittleLEC
- M.E. Clock
ME Workshop
- An Adcock
- & Shipley
- Horizontal
- Mill
Subscribe Now
- Great savings
- Delivered to your door
Pre-order your copy!
- Delivered to your doorstep!
- Free UK delivery!
All Forum Topics > Workshop Tools and Tooling > Tachometer design