user17003: I have a plant growing box, fully controlled with arduino.
Youtube: ESP8266 IOT Flora
All things are under control, besides the air temperature.
I can cool it down running fans, but cannot find a way to heat it up.
Need to keep the temperature between 25-28 C all the time.
I was thinking of:

8x8 (64) Leds - maybe this can heat up the temperature, how much ?
Dedicated Module - is there any 5v heating module available ?


user2967: The total current of your power supply, 5V • 3A is only 15 watts. That's not enough power to create a meaningful amount of heat. (although looking at your video your grow box is really tiny...)
LEDs are a terrible choice for providing heat. They produce mostly light, and very little heat (which is good if you want light, but bad if your goal is to build a heater.)
You probably want 30-60 watts of heat. As others have said, you could use a light bulb with a relay to control it. You could use a digital thermometer like a DHT11 to measure the temp, and then have a "digital" relay to control the heat source. You'd write a sketch that would turn your heater on at slightly above your minimum temp and turn it off at slightly below your max temp. (How much above and below your thresholds should be would depend on how strong your heater is and how long it takes to heat up your grow space. You'd need to do some testing.)
I created a forced air "boot dryer" where I used a couple of 120V, 500 watt heating elements in series (which lowers the power to 250 watts) and a thermostat. That is likely way too much heat for your tiny grow-box. Here is a link to that heating element: https://www.amazon.com/gp/product/B005RG64LQ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
And for a relay I used a 5V "digital" relay like this one: https://vetco.net/products/single-relay-module-for-arduino?gclid=EAIaIQobChMIgfy8jtjJ4wIVA5-fCh2TXQH1EAQYBCABEgI3mfD_BwE

user57281: You can use nickle chrome wire to easily heat that small box.
From Wikipedia:

Almost any conductive wire can be used for heating, but most metals conduct electricity with great efficiency, requiring them to be formed into very thin and delicate wires in order to create enough resistance to generate heat. When heated in air, most metals then oxidize quickly, become brittle, and break. Nichrome wire, however, when heated to red-hot temperatures, develops an outer layer of chromium oxide, which is thermodynamically stable in air, is mostly impervious to oxygen, and protects the heating element from further oxidation.

5V nickle chrome wires are available online to order, it's usually used as car seat heater.
Just be careful do not use Nickle chrome wire with Arduino directly because it can draw up to 2A from the power source and burn your Arduino board, instead use a relay to control the heater.
Here's the schematic to control a heater using Arduino and a relay:

simulate this circuit – Schematic created using CircuitLab

user31105: LEDs are not really efficient for heating up, you can better use a normal light bulb for that (they are less efficient, thus giving more heat).
The Arduino can only control some 100's of mA, that's not much for heating purposes.
Did you think about using a real heater (maybe small size), and use a relay to turn it on by your Arduino, and using a temperature sensor to switch it off above 28 and switch it on below 25 (or a lesser margin to keep up with the time it takes to change the environment temperature)?
If you do not want an external mains power, you could use probably a 12V heater and use a 12V->5V converter for your Arduino, or use a 5V heater pad, but according to what I have seen they are more for warming up cold hands, I doubt they can bring up the heat to 25-28 degrees Celcius. Besides, they are probably not very efficient.

17003: <p>I have a plant growing box, fully controlled with arduino.</p>

<p><a href="https://www.youtube.com/watch?v=6N50UWrwcsE" rel="nofollow noreferrer">Youtube: ESP8266 IOT Flora</a></p>

<p>All things are under control, besides the air temperature.
I can cool it down running fans, but cannot find a way to heat it up.</p>

<p>Need to keep the temperature between <strong>25-28 C</strong> all the time.</p>

<p>I was thinking of:</p>

<ul>
<li>8x8 (64) Leds - maybe this can heat up the temperature, how much ?</li>
<li>Dedicated Module - is there any 5v heating module available ?</li>
</ul>
 2967: <p>The total current of your power supply, 5V • 3A is only 15 watts. That's not enough power to create a meaningful amount of heat. (although looking at your video your grow box is really tiny...)</p>

<p>LEDs are a terrible choice for providing heat. They produce mostly light, and very little heat (which is good if you want light, but bad if your goal is to build a heater.)</p>

<p>You probably want 30-60 watts of heat. As others have said, you could use a light bulb with a relay to control it. You could use a digital thermometer like a DHT11 to measure the temp, and then have a "digital" relay to control the heat source. You'd write a sketch that would turn your heater on at slightly above your minimum temp and turn it off at slightly below your max temp. (How much above and below your thresholds should be would depend on how strong your heater is and how long it takes to heat up your grow space. You'd need to do some testing.)</p>

<p>I created a forced air "boot dryer" where I used a couple of 120V, 500 watt heating elements in series (which lowers the power to 250 watts) and a thermostat. That is likely way too much heat for your tiny grow-box. Here is a link to that heating element: <a href="https://rads.stackoverflow.com/amzn/click/com/B005RG64LQ" rel="nofollow noreferrer" rel="nofollow noreferrer">https://www.amazon.com/gp/product/B005RG64LQ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&amp;psc=1</a></p>

<p>And for a relay I used a 5V "digital" relay like this one: <a href="https://vetco.net/products/single-relay-module-for-arduino?gclid=EAIaIQobChMIgfy8jtjJ4wIVA5-fCh2TXQH1EAQYBCABEgI3mfD_BwE" rel="nofollow noreferrer">https://vetco.net/products/single-relay-module-for-arduino?gclid=EAIaIQobChMIgfy8jtjJ4wIVA5-fCh2TXQH1EAQYBCABEgI3mfD_BwE</a></p>
 57281: <p>You can use nickle chrome wire to easily heat that small box.</p>

<p><a href="https://en.wikipedia.org/wiki/Nichrome" rel="nofollow noreferrer">From Wikipedia:</a></p>

<blockquote>
  <p>Almost any conductive wire can be used for heating, but most metals conduct electricity with great efficiency, requiring them to be formed into very thin and delicate wires in order to create enough resistance to generate heat. When heated in air, most metals then oxidize quickly, become brittle, and break. Nichrome wire, however, when heated to red-hot temperatures, develops an outer layer of chromium oxide, which is thermodynamically stable in air, is mostly impervious to oxygen, and protects the heating element from further oxidation.</p>
</blockquote>

<p>5V nickle chrome wires are available online to order, it's usually used as car seat heater.</p>

<p>Just be careful do <strong>not</strong> use Nickle chrome wire with Arduino directly because it can draw up to 2A from the power source and burn your Arduino board, instead use a relay to control the heater.</p>

<p>Here's the schematic to control a heater using Arduino and a relay:</p>



<p><img src="https://i.stack.imgur.com/ePuOl.png" alt="schematic"></p>



<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fePuOl.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>
 31105: <p>LEDs are not really efficient for heating up, you can better use a normal light bulb for that (they are less efficient, thus giving more heat).</p>

<p>The Arduino can only control some 100's of mA, that's not much for heating purposes.</p>

<p>Did you think about using a real heater (maybe small size), and use a relay to turn it on by your Arduino, and using a temperature sensor to switch it off above 28 and switch it on below 25 (or a lesser margin to keep up with the time it takes to change the environment temperature)?</p>

<p>If you do not want an external mains power, you could use probably a 12V heater and use a 12V->5V converter for your Arduino, or use a 5V heater pad, but according to what I have seen they are more for warming up cold hands, I doubt they can bring up the heat to 25-28 degrees Celcius. Besides, they are probably not very efficient.</p>
