[Repeater-Builder] Re: temperature control circuit
At 1/8/2007 15:22, you wrote: Hi Bob, I would like to get a copy of that circuit if you have one available. Thanks, OK, here is the circuit I used. The original National Semiconductor circuit had a 30 K resistor in series with a 400 uF cap., both in parallel with the 100 K resistor on the input of the 1st LM324 section. I found that combo to actually destabilize the operation of the controller for this particular application, so I removed them changed the 2 uF cap in series with the 10 megohm resistor to 5 uF. That cap is a non-polarized paper capacitor; I believe a 4.7 uF non-polarized ceramic should work as well. The 1/4 watt heater resistor LM34 temperature sensor are mounted on the same side of the crystal but separated as far apart as possible. Bob NO6B 445.46 TX temp. stabilization.png Description: PNG image
Re: [Repeater-Builder] Re: temperature control circuit
Thanks for sharing your circuit, Bob... Have you done any measurements to see how constant the temperature is maintained over time? Looks like a neat little circuit for a couple of other applications. 73, Tony W4ZT [EMAIL PROTECTED] wrote: At 1/8/2007 15:22, you wrote: Hi Bob, I would like to get a copy of that circuit if you have one available. Thanks, OK, here is the circuit I used. The original National Semiconductor circuit had a 30 K resistor in series with a 400 uF cap., both in parallel with the 100 K resistor on the input of the 1st LM324 section. I found that combo to actually destabilize the operation of the controller for this particular application, so I removed them changed the 2 uF cap in series with the 10 megohm resistor to 5 uF. That cap is a non-polarized paper capacitor; I believe a 4.7 uF non-polarized ceramic should work as well. The 1/4 watt heater resistor LM34 temperature sensor are mounted on the same side of the crystal but separated as far apart as possible. Bob NO6B
Re: [Repeater-Builder] Re: temperature control circuit
At 1/11/2007 08:38 AM, you wrote: Thanks for sharing your circuit, Bob... Have you done any measurements to see how constant the temperature is maintained over time? Looks like a neat little circuit for a couple of other applications. 73, Tony W4ZT Measuring the LM34's output, it was very good: less than 0.2 °F change. Keep in mind that other applications will probably require a different feedback loop. The 400 µF cap 30 k resistor I removed across the 100 k resistor were probably for controlling much larger systems with longer time lags between the heater sensor. Bob NO6B
Re: [Repeater-Builder] Re: temperature control circuit
At 1/11/2007 06:48 AM, you wrote: The 1/4 watt heater resistor LM34 temperature sensor are mounted on the same side of the crystal but separated as far apart as possible. I forgot to mention that thermally conductive epoxy was used to mount the LM34 51 ohm 1/4 watt heater resistor onto the crystal. Bob NO6B
Re: [Repeater-Builder] Re: temperature control circuit
This thread is now a web article: http://www.repeater-builder.com/construction-proj/no6b-crystal-heater.html Kevin Custer Bob Dengler wrote: At 1/11/2007 06:48 AM, you wrote: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII The 1/4 watt heater resistor LM34 temperature sensor are mounted on the same side of the crystal but separated as far apart as possible. I forgot to mention that thermally conductive epoxy was used to mount the LM34 51 ohm 1/4 watt heater resistor onto the crystal. Bob NO6B
