Digital Pot setup

[CDRIVE]

You're going to want a single ended (single supply voltage) opamp. The OPA134 is a low noise, wide bandwidth amp that should work well. It's also an excellent choice for very low signals like microphones. Even the old and very common LM224 or LM324 will work fine in your application. They're all single ended supply compatible.

Google the data sheet for these and download them.

Chris

 

[JPU]

Hi Chris

Thanks for the Voltage divider schematic, I will alter my Voltage Divider tomorrow and test.

I can pick up a LM741 tomorrow from a local store. Will this do the job?

Justin

 

[CDRIVE]

The LM741 is not a single ended OpAmp. It requires a + & - 12V supply.

Chris

 

[CDRIVE]

Justin, I checked out the data sheet on the LM358 that Bob recommended. It's not a bad choice for the following reasons.

(1) Output can swing down to near GND potential (+1mV).
(2) Output can swing up to the positive rail, minus 1.5V.

However, Since you only have a 12.5V source (when fully charged) you have to take into account that when the battery is drained to 11V (11-1.5=9.5V) you will not be able to swing the output to 10V. If the battery drains to 10V the max output will be only 8.5V.

In short, you don't have much overhead to play with. Maybe someone can suggest a single ended OpAmp that can swing from rail to rail?

Chris

 

[CDRIVE]

Here's a way to overcome the issues I mentioned in my last post, This circuit uses two small 9V batteries and is independent of your 12V battery, It also draws so little that the batteries should last over a year or more if an off switch is provided when not in use..

Chris

Edit: Another option would be to replace these batteries with a small converter. 12V In 18 to 20V out. The LM358 can operate with Vcc = 32V Max.

 

[JPU]

Hi Chris

Ok, thanks,,,Will this item do the job.LM358N

I'm trying to source a part that my local shop can supply so that I can get on with this tonight. They dont have the items you have recommended..


If this part (LM358N) is no good I will order the parts you recommend.

Regards

Justin

 

[CDRIVE]

Hi Chris

Ok, thanks,,,Will this item do the job.LM358N
<snip>
Justin

Yes, I believe so.

Chris

 

[JPU]

Hi Chris

I picked up two today. The op amps I have are kia358p. I guess these are the equivalent as that is what the guy at Maplin came up with.

Here is the PDF, http://www.datasheetcatalog.org/datasheet/kec/KIA358P_S_F_FK.pdf

I have already melted one of the op amps having a go my self. I haven't a clue really how these wire up. If there is any chance you can draw a rough schematic I would be grateful. If you just show me how to double the input, ie 2V going in and 4V coming out Im sure I will then be able to work it out.

As always any help will be gratefully appreciated.

My new controller from Maxon has arrived today and I have spoken with the Tech guys there who say I do need a Voltage 0 - 10V to get the full range. I don't really want to mess about with this controller as it cost me nearly £300 so I want everything to be perfect before I attempt to wire it up.

Regards

Justin

 

[CDRIVE]

What? I already gave you one here!
https://www.electronicspoint.com/digital-pot-setup-t248126p17.html#post1472431

Chris

 

[JPU]

Hi Chris

Sorry,, I don't know what happened there. I didn't see your post!

I must of posted to an older page on my Desktop without refreshing as I didn't see that you had posted. Ill give it a try..

At the moment, I am trying to get this Maxon controller to turn my motor,,,,nothing happening and I am using it with caution!

The wiring is very complicated!!!

Thanks for your op amp post Ill have a fiddle.

Just

 

[CDRIVE]

It's a pity that you smoked one of those chips because I posted that yesterday, before you purchased them.

Chris

 

[JPU]

It's a pity that you smoked one of those chips

Chris

It ain't the first and it sure won't be the last!!!

I finally got the controller to work after 25mins on the phone to maxon....hard work!!!

Anyway, I'm now going to put all I have learned from you guys (especially Chris) to good use and start on the circuit and build.

As soon as I have something to show I intend to post Pics and videos of the design and tool. I will also show some video of the tool in action. (I hope). At least it will bring a nice conclussion to what has been a journey for me from through to almost .

Thanks
Justin

 

[CDRIVE]

Justin, here's some useful free software for ya.

http://www.tina-ti.software.informer.com/

http://www.ti.com/tool/tina-ti

http://www.filerex.com/get/windows/education/science/ltspice_iv.html

Chris

PS, Your wife is really going to hate me!

 

[JPU]

Hi Chris

I have built the circuit using the protoboard and it all works perfectly. I will post on Youtube later. I`m waiting at the moment for the bigger motors to arrive from China which are due the end of this week, then I can do a Live test ie on a horse!. I have already spoken to a local company who can machine using 3D lathes so they are going to build the motor housing when the motors arrive. They will also be constructing the control box. All I will have to do is put the guts in...

Thanks for the Tina info, I have had a look and will have a play.

If you get a 10mins can you take a look at this thread I have started.
https://www.electronicspoint.com/mosfet-irf540a-circuit-t249238.html

I have an existing product that I sell, headlights for equine dentistry. They are very popular in the profession as they are extremely bright and last for hours all from one charge. I thought I would be clever and remove the only weakness that they have and thats the switch. Its housed in rubber which wears through. I have devised a method using the PICAXE 08M2 using the adcval to sense a small current across your finger when you touch two metal contacts. The pic then switches on or off accordingly a MOSFET. Please take a look.


I don't understand why the LED wont burn bright and any help would be appreciated.

Regards

Justin

 

[JPU]

Here is the Youtube video. I have created the Proto board linked it upto the controller. It was a rough video. Once the I have arranged all the housings, I will create a more detailed video.

Justin

 

[CDRIVE]

Justin, the video is marked 'private'.

Chris

 

[CocaCola]

I have an existing product that I sell, headlights for equine dentistry. They are very popular in the profession as they are extremely bright and last for hours all from one charge. I thought I would be clever and remove the only weakness that they have and thats the switch. Its housed in rubber which wears through. I have devised a method using the PICAXE 08M2 using the adcval to sense a small current across your finger when you touch two metal contacts. The pic then switches on or off accordingly a MOSFET. Please take a look.

Don't most 'dentist' even in the veterinary field wear gloves? Gloves that would negate the use of most touch switches?

 

[CDRIVE]

Don't most 'dentist' even in the veterinary field wear gloves? Gloves that would negate the use of most touch switches?

Ah, now there's a reason why capacitive touch would be preferable.

Good call!

Chris

 

[JPU]

Don't most 'dentist' even in the veterinary field wear gloves? Gloves that would negate the use of most touch switches?

This is true! and something I overlooked!!! Not all horse dentist do wear gloves, however I do and I should have thought of this!!!

Originally I had it working using a light dependant resistor, but then I thought what if the operator needed to use the light at night? There might be a problem in the resistor sensing the difference between "the dark of the night" and "the dark of the finger". That's why I then decided to use the touch switch? I got lost in the excitement of using the PICAXE to solve what has been a pain in the butt!

If you have any other ideas, Id be interested.

Chris



I have enabled the Youtube video for public viewing,sorry, my mistake.

Justin

 

[CocaCola]

May I suggest a membrane pad switch if you are having wear issues, using the micro to latch the momentary contact when pushed... The current membrane pads are some tough puppies and take a ton of abuse... If you put the micro to sleep and use a wake on change interrupt to do the latching, the battery consumption will be nil, a lot less then constantly monitoring a touch switch...