Guess what.....the one in the working machine is also dead.

 

With only one machine left i would be measuring what its thermistor resistance is a t about 25Deg C, before there is none left on the Maldives.

 

If RIFAA is writing the code for these anyway, can't he just use his own Thermistor value?

Or was his code timer based only, and not dryness based?

 

I have several of these 2K ohm @ 25Deg C thermistors for free if they are any use. The botom one in the picture. They are used in motor vehicles to sense the coolant temp for the ECU. So they are rugged & with plug. If they are usable PM me.

 

Hot digidydo..
@Debe..........tht's just what I need.

But wait ..I have to show u guys something. Got to get me camera back.

Still trying to find them thermistors from my junk yard.

The thing is, I need to have a stock on what I will use in the prototype.
So I need atleast say around 5 pcs of the same type for warranty purpose

Oneguy dear...I have yet to write the code. I need to have a thermistor to built the RTD amplifier u know.
I am really buzy these days..

 

The Test one is giving me flashing LED's but it was not supposed to do that.

Good thing it was wired like that. Had a hunch on the contacts giving up.

See the relay contacts

I believe it is due to 'em switching contactor coils which is inductive.

I used the original relays that came with the Dryer PCB.

How would I avoid this happening in the future ?

So Now I had to replace them with the ones I bought for the Prototype I was making.

 

If the contacts are switching LV DC, put a diode across the inductive load & it will give beter contact life. I am asuming these little relays are switching larger ones?

 

Contacts use 220VAC.

 

The relays look to small to be switching any sizable load as they are only about 2A. So what are they switching? After looking at the atachments, it would apear these small relays are switching larger relays that have 240V coils. You could try VDR/surge arestors across the small relay contacts, thus reducing the arcing. Such as MOV. 20D781K Vrms AC 275. Imax 10000.

 

I wonder how hard it would be to fil your new relays with as close to pure Nitrogen as possible. A fill valve and an output only check valve.

DIY cheaper than a vacuum breaker.

 

OK...here is another Idea I got.

Since the thermistor faulted and it is like whatever the reason may be, it is always too difficult to find what you are looking for. So to get rid of this headache I decided to make the temp measurement circuitry separately.

No more numerical digits but just a bar graph to display the temp rise.
With a fixed Vcc and the LED voltage used as the limit, I can make it modular.
So say in the near future the thermistor decides to got to hell then I can just plug out the module, make another with the thermistor that is available then and plug it in to the Controller.

How's that ?

This method also makes the coding much easier ...NO ?

 

That'd work, as long as the people understood the new user interface.

I'd be sure to get a can of Good conformal coating shipped to you as well to spray over all the boards before installation, that is just too much corrosion.

 

That'd work, as long as the people understood the new user interface.

I'd be sure to get a can of Good conformal coating shipped to you as well to spray over all the boards before installation, that is just too much corrosion.

Ebay seller won't ship the conformal coating can...I tried to buy before from UK as I recall.

 

I've tried to make a block diagram of what is going on. Am I way off track with this:

 

OK... so I am going to go with LM35.

The environment is noisy so I am using a shielded cable for the signal path.
Just look at the pics and guess the works... Really really bzy to keep writing stuff.
Besides you are guys should know somethings when you look at it.

The LM35 is prepared to be inserted into the tube which housed the original thermistor, or which was the original thermistor or ..ummmm ..anyways, I checked the signal voltage rise just to make sure that I do not mess it up after I apply the thermal Glue.

Which you can see below

The glue is Awesome....rock solid and the Signal value is same as a standalone one. ...

Ummm....Dad took the thermistor with him tonight. I forgot to take it out of the cycle storage, I went to buy some heat resistant tubes and forgot to take em....so later.

 

Looks good.

Lets hope you managed to fill the little tube completely, so there is no air inside.

 

OK..So I manage to make a sensor using the LM35 and it works pretty well.
I checked the sensor out by putting it into water, and slowly heating the water, I measured the sense voltage It rises as per the data specs.

From 0.25V to 0.93V which is the range I need to make a bar graph display.
0.93V is at 200°F which by the way is a bit over the max range which will be used for over temp. alarm level.

The bar graph circuit is half way drawn and I need to add the over temp, LOW &HI level temp circuit's which will be used to trigger the PIC inputs.
Which will trigger the necessary outputs and also alarm if abnormal temp.

Look at the my first design. The 7 segs are mot yet added but the rest is how it will be. The circuit basically activates timed outputs. 40min, 30min & 10min dryer cycles. The Cycles will start to count down once the Dryer Air temp reached the LOW level. The heater will cuttoff when HI level is reached and it will cycle in between these two levels.

First I like someone to correct me the circuit timing crystal or will it be accurately timed.

Second I need someone to help with the coding to drive the 2 digit (multiplexed) as it count downs the inputted cycle.
I am willing to pay for the coding who ever it is. But please let me know the price first so I can include it in the quotation. I will be using PIC's for this design.

Thirdly I like to ask do I need to use another PIC with more pins or will it be easier to use 1 pin to scan all the input keys and use the rest for the purpose described below.
The PIC labelled in the diagram has 18 pins. I need more pins to input alarm circuit outputs, to generate two digit error codes to indicate faults such as over temp, sensor open, door open, and the four relay malfunction errors (I have found that the relays used in it creates contact faults over time).

So my question is, do I need more pins or would the current PIC suffice.

Thanks

 

Just i quick thought: Could you use a BCD to 7-segment IC? Then you could use pin15-17 for input. Also, is it possible to use the internal oscillator instead of the crystal? Save even 2 more pins. If this is doable, you have 5 pins for input.


Just a thought...

 

great Idea jens..

 

About programming:

What if we start with a "Flow-chart"? To tell the operation of the program.