How do I design a circuit that will vary the intensity of a heating element over a 24hr period?

I am designing a 'heat box' for a college project, and basically I need to be able to control a heating element in such a way as to mimic the suns intensity on a typical day. so for example the heating element needs to come on at about 6 am at a low intensity, the intensity needs to slowly increase until say midday ( when it should peak) and then tail off until nightfall. any ideas?

sort by: active | newest | oldest
kikiclint8 years ago
Use a relay to control the mains power to the heating element, and then use your computer or a microprocessor to change a duty cycleI( how long the power is on during a cycle) As long as there is enough thermal mass, and the frequency of the duty cycle is high enough this should control it well. A temperature probe could be used to make sure the temps are in the right range as well. All you would need to do is program when you want the temperature to change
Ah ha ! How about converting a thermo electric fridge ???? Heat cool, power control, all in one place....
seandogue8 years ago
You have the basic gist. If you want to mimic the sun, it might be of value to obtain hourly temperature data for a "typical" day from NOAA or a local source like the tv station... Better even would be to measure it yourself, using a datalogger or similar. Once you have that data, you can program a PWM or alternative heater control using a programmable controller or PC and controller to adjust the heating element's response to a given hour, in order to mimic the data. For instance, suppose you lived in a county of Northern California, you could mimic the temperature profile of your area by using the garnered data as control settings, then use the heating element and temperature sensor to provide input and output to and from the control loop. The temp sensor is required so that you can compare it's value to the recorded data and generate an error value to increase or decrease the heating. A better solution will use some form of cooling as well. A simplified control system (avoiding designed and implementing your own controller) will use a canned heater control, with temperature feedback, setpoint selection (that would be the output from your computer). The heater controller should provide both heat and cool functionality to drive the heater and fan.
Truth is, you could easily do more than mimic the day,..you could track it...simply use a temp sensor mounted externally (outside that is) as your control source (setpoint)...
As long as the temp outside exceeds the indoor temp that is...beyond that you'll need more than fans for the cooling cycle
How accurate do you need ? Making it isn't too hard, if you use a feedback loop.