Ok then ...let me finish up a rough schema.

 

So..Here is what I cooked up, not finished yet.
This is the basic idea. The thermistor part is yet to be drawn once I measure the resistance change with applied heat.

For the curious minds

#DSW-3 is an input coming from the Door switch. This supplies the power to the contactors via the relay contacts. The relays are not yet shown as they are not on hand. I have bought 9V Relays & they have been shipped.

This voltage absence also halts the program when the door is open and resumes when closed, so I figured the interrupt would be best.

The switches are pretty straight forward. DR1 to DR3 are the three dry cycle user inputs.

Bu
DR1 - is the 10 minute dry cycle
DR2 - is the 30 minute dry cycle
DR3 - is the 40 minute dry cycle

Start and stop should do what the switch says.

The LED1 to 4 will be on the PCB and is an indication of proper operation. Relays will be connected to TP points.

Buzzer is a 5V continues beep type, I guess it will beep when power is applied.
Buzzer should sound after a dry cycle ends or the door is opened.

I haven't yet started on the code. Really need time to get these things going. Since I repaired that BoxX PC's mobo & PSU, those guys are calling me 24/7 with all sorts of things to fix . Everything they have been piling up is now on queue.
What can I say. They pay handsomely .

If any one takes the initiative with the code please let me know, if you like to see my 40min dry cycle codes for the basic idea. Like to tell that member won't regret it, this I promise.

PS. I like to know what would the price range for a typical coding and circuit building that you guys do..Since this is my first attempt I like a heads up on what I should demand for this job.

The schema is posted cause I want some one to comment on it. Need to improve. That place has lot's of noise and transients.

{ed}
Holy Crap...!! I just remembered, the F88 is not good for the job, right. I need more pins to display the time with 7 segs.
Oh well ! back to the drawing board...

 

Can any one clarify this problem.

It's about the Dry cycle count down timer. It should be timed accurately, so in order to do that, the oscillator should be stable , right.

I have to chose another pic with more pins but don't know what oscillator to use.
in order to get the 1 second clock, which oscillator is good.

which is best for 1 sec timings , the internal oscillator or to use an external crystal ?

 

Probably the internal oscillator is fine, for the 16F88 the maximum error at 5V and 25 celsius is 2% which is 1 minute in 50 minutes.
For -10 to 85 celsius the maximum error is 5% which is 2min 30.
Probably the error will be much less.
Different PICs have different frequency accuracies so worth checking on your choice.

 

OK ..Finally.
This would be the schema I will go with as I have this typical PIC...

 

Can any one care to tell me how to begin this thing?
I mean..oh wait lemme start learning C Code

Me paid for this

 

To complete the circuit I need to find the sensor temp variation data.
So I brought one sensor.

But this thing is not showing any resistance nor any voltage variation when heated.
Note: Nominal R is Open circuit. ( I think it is faulty )

I have attached high res photos so you can try to make out what is written on it.
Cause I cannot make out anything from this.

Photo's are of different angles

1 2 & 3

 

For an accurate timer using a PIC, check out Roman Black's page:
http://www.romanblack.com/one_sec.htm
That combined with an OCXO:
http://www.romanblack.com/xoven.htm
will allow you to make a timer that is accurate enough that nobody will complain.

The thing about a timer for commercial purposes is, that if the time runs too short, and people are paying for it, the owner risks getting sued. If the time runs long, then the owner will have more expense for electricity and maintenance on the equipment.

You might as well avoid all of those "unhappy problems" and just make the timer accurate to begin with.

 

Sgt....I am concerned about the sensor...it's open and I cannot tell what type it is.

 

Sgt....I am concerned about the sensor...it's open and I cannot tell what type it is.

Can you compare it to a known good sensor from another dryer?

Or from the patent?

I's suggest switching to the PIC16F690, it gives you... everything for a General Purpose, 10 ADC, or Comparators, or PWM, 17 I/O + 1 input only for a total of 18 In and 17 outputs (in a 20 pin package).

Don't bother with the 16F88, this is the upgraded version, and once you disable comparators and ADC, programs just like the other 16F6xx series for the most part. porta and portb are 5 bits each, portc is full 8 bit.

Enough with that sidetrack...

Compare that device with one from another working dryer, using a heatgun. It could be open/close@temp, or a thermistor, or even a low temp thermocouple. What was it going into on the original board? That will give a hint of what type sensor it is.

 

Hello,

If the dryer is gas heated, also check if the burner is giving a flame.
Otherwise the gas will give huge problems.

Bertus

 

Can you compare it to a known good sensor from another dryer?

Or from the patent?

I's suggest switching to the PIC16F690, it gives you... everything for a General Purpose, 10 ADC, or Comparators, or PWM, 17 I/O + 1 input only for a total of 18 In and 17 outputs (in a 20 pin package).

Don't bother with the 16F88, this is the upgraded version, and once you disable comparators and ADC, programs just like the other 16F6xx series for the most part. porta and portb are 5 bits each, portc is full 8 bit.

Enough with that sidetrack...

Compare that device with one from another working dryer, using a heatgun. It could be open/close@temp, or a thermistor, or even a low temp thermocouple. What was it going into on the original board? That will give a hint of what type sensor it is.

For the PIC, I will see to it.

As for the sensor.
I have given a temporary solution. And two is running at peak load. Can't shut down even one to take out the sensor.

I have to see the service manual or contact ADC.

And Bertus, it is an electric one. We don't have gas supplied like in ur states.

If it were this place will be on fire 24/7.

 

I would bet the thermistor is a NTC sealed type, Usualy there resistance is quoted at a temp of 25Deg C. No clues to value in the documents just says replace if faulty. Only way is check the resistance of a good one in another dryer. Its only sensing temps in the range of 20-93deg C.

 

So i thought...
Debe have u seen anything like this closeup?

 

I am concerned about the sensor...it's open and I cannot tell what type it is.

I am uncertain. Thermocouples frequently have metallic casings, so if I had to simply make a wild guess, that's the direction my guess would go. However, it would be better to examine the signal input for the temp sensor; you could probably get a good idea by reverse-engineering that.

If it's an instrumentation amplifier alone, then a thermocouple would be the most likely answer. If there is a current source for the temp sensor, then a thermistor or semiconductor sensor (maybe even a simple diode) would be more likely. If it is a digital IC of some sort, then it may have an internal digital sensor, like a DS18B20 - however, those usually require 3 wires.

 

<sniiiiip>
{ed}
Holy Crap...!! I just remembered, the F88 is not good for the job, right. I need more pins to display the time with 7 segs.
Oh well ! back to the drawing board...

Have a look at Roman Black's page on the shift1 system. If you just have 1 I/O pin to spare, you can use that to display whatever you want. It's a bit slow though.

http://www.romanblack.com/shift1.htm

 

Hello,

If the sensor has about 100 Ω at 25 °C, it could be a PT100.
There are also PT1000 sensors around, those will measure 1000 Ω at 25 °C.

Bertus

 

Hi R!f@@. Thermocouples generate a DC voltage when heated. resistance check will read 1-7 ohms aprox. Pictures of 2 NTC thermistors . The one with the bracket is out of an oven & reads 300K ohm @ 25 Deg C. The other one reads 10K Ohm @ 25 Deg C. Ones in my Fridge are in a plastic tube & are 2.5K Ohm @ 25 Deg C. As you can see they come in a vast range of resistances.

 

So we are not sure what the Dryer has, right ?

 

If you are designing a new controller then it doesnt matter what u use for a temp sensor. So long as it will handle the temp range of 20 / 93 Deg C, this is what the drier is looking for. Just that when fitting your controll, you fit your new temp sensor.