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Temperature-controlled Light Dimmer for Reptiles

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Olihou

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I have the interest to build a Temperature-controlled Light Dimmer for Reptiles (desert tortoises).

As a natural instinct and probably for the sake of good health desert tortoises like many other reptiles enjoy basking in the sun. However in the reptile house sunshine is a scarce luxury and therefore artificial light (tungsten filament lamps) have been used. Just as in the nature, the tortoises will seek shelter from the "sun" when they have enough "tanning", or when the ambient becomes too hot. Due to the limited space again, the tortoises may not be able to "escape" entirely from the hot "sun". The lamps would need to be turned off or dimmed down.

I have therefore had this idea : let the lamp be dimmed down when ambient goes beyond 30 DegC, dimmed futher when ambient goes up to complete shut-off say beyond 37 DegC. The change should be smooth, i.e. no sudden on or off of the lamps (i.e. no lightning/thunders!).

I have never seen in the market anything that can do the job, nor have I seen any published work on this.

I believe that a simple circuit, without MC, should be able to do the job. I have found many dimmer circuits on the web, but they are manual, and not temperature controlled. There are also a lot of temperature-control or thermostat circuits, but are always employing simple relay or triac on-off switching. We need to combine these two kinds of circuits.

It seems to me no one has ever done such a design yet.

Any advice or comments please ?
 
If it's for tungsten lighting only, I suppose you could use a standard lighting dimmer, but replace the control pot with an NTC sensing element, if you can find one with an RT curve in a suitable range for your needs.
 
Thanks.

It is indeed a simple but effective solution if, and only if, I can find a suitable NTC thermistor.

I have a quick check of the characteristics of the NTC thermistors. For those with high sensitivity, the TC can be as high as -6% per Deg C. To meet with my goal the lamp needs to be turned from full on to full off with an ambient temperature rise of about 10 Deg C. However by this temperature change, the reistsance of the thermistor decreases by 60%, say from 100 kohm to 40 kohm ---- but this is by no way sufficient for a simple dimmer circuit, I wonder ?

To completely turn the lamp off, the resistance should probably drop to 10 kohm or below ?
 
I must be honest, I have never really looked into the possibility of controlling a dimmer with an ntc. The idea seems simple, but I fear that in practise it will give a poor response. I think the final solution may include a fet as the controlling element, and perhaps an opamp/ntc arrangement for temp sensing. If you were to use an opamp, I dare say that one of the temperature chips could be used, maybe the LM35, the response of that device is very linear, you could then adjust the opamp swing to be within your wanted range etc...
I'm only putting forward ideas here :)
 
To clarify my thinking in response to Tunedwolf, I have put up the attached circuitry. Would it really work ? Values for R and C appropriate?

I start to feel that it may work for some sensitive thermistor RTH if a wider temperature range is allowed, say from 20 to 40 Deg C --- i.e. fully on below 20 and fully off above 40 ?


Comments and suggestions please !
 

Attachments

  • Temp Control Dimmer.GIF
    Temp Control Dimmer.GIF
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Why the need to not use an MC? Even a high powered 8 pin device can be had for less than 3 dollars. Lower powered devices can be had for approaching under 50 cents. In a case like yours where finding the properly valued analog components is the trouble it's a more stable and flexible sollution to use an Uc. Even a random NTC yanked out of a junk bin could likley be adapted to your use.
 
All you need to keep them healthy is a full spectrum lamp on one side of the enclosure and reptile heating pad under the enclosure on the other side and maybe a 60 to 100 watt incandescent black light over the heat pad side. when it wants a cool place it will move away from the pad area. take it outdoor as often as you can to get UV rays. You did not reply to my questions, so I figure you just need a project to do and not interested in keeping healthy.
Theres a co. that makes a device that will do this, let me know if you want me to find there name. dont remember off hand.
 
9volt said:
All you need to keep them healthy is a full spectrum lamp on one side of the enclosure and reptile heating pad under the enclosure on the other side and maybe a 60 to 100 watt incandescent black light over the heat pad side. when it wants a cool place it will move away from the pad area. take it outdoor as often as you can to get UV rays. You did not reply to my questions, so I figure you just need a project to do and not interested in keeping healthy.
Theres a co. that makes a device that will do this, let me know if you want me to find there name. dont remember off hand.

Thanks for your advice. I do agree with your recommendation. In fact I am doing almost the same thing as you said: one side hot pad and the other side spot lamp. I am going to add a UV lamp beside the spot lamp.

I have made the hot pad already. It is thermostat-controlled to around 35 Deg C, with triac on-off switching. My two tortoises, a Sulcata and an Indian Star, seem to enjoy very much sleeping over the pad.

The "temperature controlled dimmer" is the next thing I would like to build. It is nice to hear that some one has made a device like this already. Please do let me know more details.

Thanks.
 
A few years back I had 44 tortoises. 5 breader pairs of sulcatas they alone would eat 10 boxes of produce a week.
had only one pair of Indian stare. they were my favorite. I will find info for you and send asap.
 
Sceadwian said:
Why the need to not use an MC? Even a high powered 8 pin device can be had for less than 3 dollars. Lower powered devices can be had for approaching under 50 cents. In a case like yours where finding the properly valued analog components is the trouble it's a more stable and flexible sollution to use an Uc. Even a random NTC yanked out of a junk bin could likley be adapted to your use.

Why not MC ? Because I am not equiped to use MC at present.

I am interested to, but it is probably more a long term project for me. I need to first find out what MC to use, than purchase the development kit, start understand the MC, then code, then burn and then assemble .......

For the time being I am eager to build the device quickly from off-shelf components, before the arrival of the cold weather.

However I would be grateful for your advice on a "low-cost" and "quick-start" approach to using MCs please ?

Thanks.
 
9volt said:
A few years back I had 44 tortoises. 5 breader pairs of sulcatas they alone would eat 10 boxes of produce a week.
had only one pair of Indian stare. they were my favorite. I will find info for you and send asap.

Wow ! 44 tortoises ! Impressive !

I have the interest to take more, but not more than 10, not until one day my family moves from the present multi-storey building to a house with backyard !
 
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