Digital Pot setup

[CDRIVE]

I watched the vid. Someone's having fun!

Chris

 

[JPU]

Hi Chris

When building the op amp circuit to multiply the voltage *2 , can I use 2.2m ohm resistors in the circuit in place of the 2m resistors. What are the implications.

Justin.

 

[CDRIVE]

The OpAmp will then have a gain of 2.2. Can you live with that?

Chris

 

[JPU]

The OpAmp will then have a gain of 2.2. Can you live with that?

Chris

Is that how it works!!!!???,That should be OK!

Thanks Chris

Justin

 

[CDRIVE]

Keep me posted.

Chris

 

[JPU]

Hi Chris

I'm sorry to hold you up on the mosfet thread, I haven`t had a chance yet, but hope to do it tomorrow.

I need a little help though. I have been working on this motor step up/down circuit and have made some alterations due to the new battery voltage ie 29V

I have been testing the system all week and its been working well, in the field. However I have made a slight alteration to the program, so that the LED flashes twice when the slowest speed is reached, I have been getting odd results and I have realised its due to the fact that the 5V regulator is only rated up to 25V. Do you know if its possible to get a regulator that will produce the 5V I need but will work with a 29V-20V battery. I appreciate that you may think "go take a look yourself!", but there are so may other permutations in the data sheets that are way beyond my understanding.

Your help is appreciated and I will get those results to you tomorrow.

Regards

Justin

 

[CDRIVE]

You can replace it with an LM317. A quick hack, if you have one, is stick a 12V Zener in series with the input pin of the 7805. If you do this I'd also connected a 4.7KΩ from the input pin of the 7805 to ground. A 1uF cap in parallel wouldn't hurt either.

Chris

 

[JPU]

You can replace it with an LM317. A quick hack, if you have one, is stick a 12V Zener in series with the input pin of the 7805. If you do this I'd also connected a 4.7KΩ from the input pin of the 7805 to ground. A 1uF cap in parallel wouldn't hurt either.

Chris

Hi Chris

I took a look at the LM317, Im not sure how I can get that to work and it may require more componets?? its says in the tech spec that its variable output??

I have had a look at the Farnell site and I have found this

http://uk.farnell.com/micro-commercial-components/mc7805ct-bp/ic-ldo-reg-5v-1a-to-220/dp/1924634

ie. MC7805CT-BP

Will this do as a simple out with the old, in with the new swop, job done!

Justin

 

[CDRIVE]

Aren't you already using a 7805? That number is just another variant of the same. Vin Max is 30V so you'll be pushing it to its limits. Do you have any Zeners laying around?

Chris

 

[JPU]

Chris

I do have a couple in my box. I'm not sure about the voltages I'll check. If not I'll pick up some 12v zenors today.

I've got the day off today to work on the project. I was looking forward to some peace and quiet to get some work done but I should have know that was wishfully thinking. My 2 year old daughter is now spending the day with me, home from nursery with a temperature. That means a day of nurse maiding , lots of tears and demands for pepper pig!

Definitely no peace and quiet!

Justin.

 

[JPU]

Chris

They have 12v and 13v zenor at the store. They only have 1 * 12v. Can i use the 13v as well as i have 3 to adjust and will I need a different size resistor.

Justin.

 

[CDRIVE]

Yes 12V or 13V will work but I have a Question. This is to power the 7805 and then the Picaxe. How are you powering the OpAmp? You're not powering the OpAmp off the 30V rail are you? If that's the case, scrap the Zener idea and get a 7815 regulator. Power the input of the 7815 from the 30V rail. Power the OpAmp and 7805 from its output pin. This will give you a regulated 15V to the OpAmp and a better way of stepping down the voltage to the input of the 7805.

Chris

 

[JPU]

The OP Amp is being powered by the battery. I will go down the suggested path.

Thanks

Justin

 

[CDRIVE]

Yes Justin. Never run a device to its maximum limits. That OpAmp is rated for 30V Max.

Chris

 

[JPU]

Hi

I have been testing the device now for a couple of weeks and its been working a treat!

I have been to see a local electronics company and the owner was very helpful and is willing to create a "Gerber" file? for me so that I can take that to another local company to have the boards produced professionally.

If you get a moment, I would be very grateful if you could take a look at this Tina file for me that I have created (basically your schematics merged) to see if I have made any obviuos mistakes and whether you think it can be used to create the Gerber file. The chap at the electronics company was very interested in the project and in his words "as long as I can see the schematic then I can create the gerber file so that the layout will suit your project box".

Here is the file: http://dl.dropbox.com/u/7717360/final circuit.TSC

Thanks for your help

Justin

 

[CDRIVE]

At a glance it looks OK.

Chris

Edit: There's no ground on the 7805. I posted this twice, so you don't miss it.

 

[CDRIVE]

Justin, just noticed that the 7805 isn't grounded!

Chris

 

[JPU]

Chris

Thanks, I didn't spot that.


Justin

 

[JPU]

Hi Chris

I have tried to create the Gerber file myself but have found out that the free version of Tina does not allow you to do this. I have had a look at the Tina site and can see that the Tina design suite basic edition allows you to create Gerber files.

https://www.designsoft.biz/orders/order.php

I thought I would just ask, if you thought this would be a worthwhile purchase for me and is it easy to learn and use?

Regards

Justin

 

[JPU]

Hi

Chris, I'm not sure if you have read the above. I placed it in the wrong thread originally and then deleted the entry.

Regards

Justin.