HCH-1000-002 Circuit Design Help.

[cbiblis]

I am looking for a circuit schematic using a HCH-1000-002 ( HCH-1000 pdf, HCH-1000 description, HCH-1000 datasheets, HCH-1000 view ::: ALLDATASHEET ::: ) to control humidity ranging 10% - 90% via a Pot. I will use the circuit in my chicken incubators to switch a 12v relay ( T7CS5D-12 Product Details - Tyco Electronics ) to interrupt the main to a reptile fogger. I would like to use either a LM324N or a LM339N for the IC because i will incorporate the circuit into my thermostat design which only uses 2 of the 4 comparators. However i could always build a different circuit PCB all together. Any help would be very much appreciated.

 

[Brevor]

Honeywell has this app note maybe you can get some ideas here.
**broken link removed**

 

[Vizier87]

they're capacitive humidity sensors, you'll need to condition them according to the circuit provided by Humirel:
**broken link removed**

Adjust the values of the R2 and R4 so that the output frequency is readable by your DMM, but PICs can read much higher frequencies depending on the clock speed.

 

[cbiblis]

Thank you both for you reply.
First off, forgive my ignorance, i am just a hobbits.
What i was wanting to do, much like my thermostat design, is to use the HCH-1000 in place of a resistor. Add a variable resistor inline to an op amp. Then to a BC547, then to a relay that switches the relay on/off.
When the sensor value is low it will switch the relay on. When the sensor value is high it will switch the relay off. Will this work in this fashion? I have a digital temp/RH meter already in my cabinets to display the internal conditions. So i was thinking to stay analog with this circuit.

Vizier,
Can i use that circuit with the HCH-1000 ? That would be good if i can. The Honeywell Frequency circuit uses a lot more components Then the one you posted. I like smaller boards.

Thanks for your help.

 

[cbiblis]

Here is what I'm thinking. I'm shooting from the hip. Please help with the boxed area or let me know what to do to make it work. Thanks

 

[Brevor]

Hi Cibibls,
I admit the circuits in that Honeywell ap note are complicated, Vizier87's circuit should be OK it works on the same principal. The circuit you posted wont work. The op amp circuit you discribe, like the thermostat circuit you use is controlled by a voltage. But the humidity circuit you want to use puts out a frequency so it cant be triggered the same way. There are ways to convert a frequency to a voltage, but offhand I cant think of an *EASY* way to do it. No one does it like that anymore, they usually use..... you may have guessed a microcontroller. Perhaps someone else on the forum knows a simlpe way to convert from freq. to V.

 

[Vizier87]

Vizier,
Can i use that circuit with the HCH-1000 ? That would be good if i can. The Honeywell Frequency circuit uses a lot more components Then the one you posted. I like smaller boards.
Thanks for your help.

Yes, I used exactly the same sensor you're using. You just need to use much higher values of R2 and R4 (I used megaohm ranged ones) because the capacitance of the HCH 1000 is very small, 1.8 pF in my room, I don't know about yours.

There are ways to convert a frequency to a voltage, but offhand I cant think of an *EASY* way to do it. No one does it like that anymore, they usually use..... you may have guessed a microcontroller. Perhaps someone else on the forum knows a simlpe way to convert from freq. to V.

Microcontrollers can handle the frequency detection, or if you want your indication to be done in Humidity-Versus-Voltage output you can use a Frequency-to-voltage converter like the LM2917.

https://www.electro-tech-online.com/custompdfs/2010/02/LM2907.pdf

 

[Vizier87]

Here is what I'm thinking. I'm shooting from the hip. Please help with the boxed area or let me know what to do to make it work. Thanks

If you wish to use the f-to-V converter, feed the output into an op-amp in comparator mode. It is much simpler to do so. For comparator configurations, look into the sticky in this forum.

Like I said, a microcontroller is good for data profiling, but since you don't seem to be a fan of it then I'd suggest the action in the paragraph above. Good luck.

 

[cbiblis]

Am i getting closer?

 

[Vizier87]

Is this just a design course? Have you tested the output of the f2v? I see that you reconstructed the f2v in the design you gave. That is not necessary. Here is the configuration, just connect the components to the pinouts to the IC from your software database for the 2917.
**broken link removed**

I think the buffer you had for the comparator isn't necessary, you can just feed the output directly into the op-amp input.
Good luck.

 

[cbiblis]

Is this just a design course? Have you tested the output of the f2v? I see that you reconstructed the f2v in the design you gave. That is not necessary. Here is the configuration, just connect the components to the pinouts to the IC from your software database for the 2917.
**broken link removed**

I think the buffer you had for the comparator isn't necessary, you can just feed the output directly into the op-amp input.
Good luck.

No i haven't tested it yet. I'm going to build it. I don't have an electronics store near me, so i have to order the parts. I figure i will get the circuit close then order everything at once to save on shipping.
Yes i had to build the f2v. i don't have the 2917 in my version of eagle. It would be nice to have thou, building it took over an hour. i need to update my library.
I looked for the pinup you spoke of and couldn't find it. i did find a couple op amp pins thou. they helped me understand the op amp a little more. As for comparator configurations, i couldn't find it. If you could post the link i would be grateful.
Thanks for your help.

 

[Vizier87]

Use this comparator:
**broken link removed**
the non-inverting input takes the output from the f2v. Adjust the pot for the threshold values of your preference, the output of the op-amp can be fed into the base of your transistor driving the relay.

I advise you to not buy only specific components for this project, but buy several other components which aids different designs.

 

[cbiblis]

what are the leds for?

 

[Vizier87]

no, you gotta omit the LEDs, I didn't adjust the circuit. look at the op-amp circuit only. The idea of a comparator is that the positive difference between the inputs are multiplied by an infinite gain, so the pot needs to be adjusted so that the voltage from the v2f is same or lower than the voltage into the inverting input. When you attain a lower humidity, v2f output gives higher voltage, creating the positive difference between the inputs.

Comprende?

 

[cbiblis]

gotcha. Thanks, i'll type it up.

 

[cbiblis]

How about this configuration? Is this what you mean?

 

[Vizier87]

no, use your previous design, it should work, I just wanted to simplify the design by omitting the buffer you incorporated in the comparator circuit. Directly feed the v2f into the pin 6 of your comparator circuit, and the comparator should be according to the circuit I provided before.

Anyway, I suggest you just buy them all now, test 'em on a breadboard. Simulations and diagrams are always deceiving. That'll save us from a lot recapitulations.

 

[cbiblis]

Ok, here it is. Notice that i added diodes to the power feeds. This was also suggested to me. Is it over kill or is it right? I am guessing that i am going to have to build the frequency and voltage converter before i can count up the resistors in the comparator circuit. Look it over one last time if you would. I will order the parts that are on the schematic today. Also would i even need the r8 for hysteresis?

 

[Vizier87]

I have no way of knowing how your supply is going to turn out. Usually people use batteries, you know.. but I suppose that question's cleared? If so, you don't need to elaborate.

Here is what I meant:
**broken link removed**

Phew!!!

 

[Vizier87]

sorry.. double posted.