318 replies to this topic

[Splunge!]

Doug,

 

 That would work, but I used this: https://www.amazon.c...product_details

 

Regards,

Edited by Splunge!, 21 August 2023 - 04:47 PM.

[Splunge!]

 OK, it's finished and tested as working, so I closed it up. Here are some final pics:

 

 In the box, ready to go...

 

 The final product....

 

 On the scope...

 

Thanks again Mark!

 

Regards,

[mlord]

Note that since you didn't go for the added complexity of the OLED and two buttons, the only way to adjust the "offset" for dew control temperature is by editing the source code and re-uploading. 

 

This line specifically:

 

static float dewcontrol_target = +2.0;

     // Degrees C by which DewRing should be warmer than DewPoint

 

Cheers!

Edited by mlord, 21 August 2023 - 05:17 PM.

[dlwmacgregor]

 And yes, you are reading them wrong - I measured them as 4.70 and 4.71K Ohms...

Now I know what the problem was. I was used to dealing with 4-band resistors in the 80's, not the 5-band ones.

[Splunge!]

 @Mark: Yes, I figured that would be needed if it didn't quite work in real life, but we will see...

 

 @Doug: Ahh! I grabbed those resistors from a box of left overs, and they very well could be 1% resistors, which I believe have an extra band...

 

Regards,

[dlwmacgregor]

 @Mark: Yes, I figured that would be needed if it didn't quite work in real life, but we will see...

 

 @Doug: Ahh! I grabbed those resistors from a box of left overs, and they very well could be 1% resistors, which I believe have an extra band...

 

Regards,

You built a stand-alone unit, right?

[mlord]

You built a stand-alone unit, right?

Yes, user "Splunge!" built an Arduino ProMicro based version that I developed for people who intend to use it on a non-Celestron mount.  So it needs a buck converter, 5V/16MHz ProMicro board, and then the usual resistors, diode, IRF520 MOSFET module, SHT30/31 sensor, various connectors etc.

 

As it turns out though, the original HBG3-based version can also be used on non-Celestron mounts too.

[dlwmacgregor]

So can I assume that I can build that same unit  for my Celestron mount even though I have the HBG3? ( I have most of the parts).

I want to use it with CPWI, as you have.

Edited by dlwmacgregor, 22 August 2023 - 10:06 AM.

[mlord]

So can I assume that I can build that same unit  for my Celestron mount even though I have the HBG3? ( I have most of the parts).

I want to use it with CPWI, as you have.

For use with CPWI, it is best to do it as an extension of your HBG3, rather than a completely new standalone unit.

[dlwmacgregor]

Would I be using the Pro Micro board as an extension or would it not be needed?

[mlord]

Would I be using the Pro Micro board as an extension or would it not be needed?

Zero need for it.  You already have a much more powerful processor to run everything.

[dlwmacgregor]

How do I put the display and SHT31 both on the I2C bus at the same time? With your new PCB that would be easy. How do I do it with the HBG3 I have?

[mlord]

How do I put the display and SHT31 both on the I2C bus at the same time? With your new PCB that would be easy. How do I do it with the HBG3 I have?

Just wire them together in parallel, pin for pin.  The Nunchuck is also on the same four I2C signals, as is the optional FRAM module that some people with Focus Motors have added.

Edited by mlord, 22 August 2023 - 12:16 PM.

[dlwmacgregor]

Here's what the solderless breadboard version looks like:

 

prototype.jpg

 

The connector at far left is the mono jack for the thermistor connection.  The big black coiled cable on the right is the SHT31 module, which is used to measure ambient temperature and relative humidity.

 

The IRF520 module looks like this (below):  It has the big MOSFET sticking out towards the camera, and a single 1K pull-down resistor for the SIG input, plus a red LED and second 1K resistor to give an activity indication.  There's a connection for Vcc, but the module doesn't actually use that for anything.  See here:  https://robojax.com/...x-IRF520-MOSFET

 

IRF520.jpg

 

The top RCA jack at left is the output to the Dew Ring, and the connector below it is a 5.5mm/2.1mm input for 12V power.  The only other components on the breadboard are a 1N5817 diode to protect GPIO4 from reverse current on SIG, and a 10K resistor for the thermistor input.  The rest is just wires.. and a HomeBrew Gen3. 

 

That's what I've been testing with thus far, and it works well enough for me indoors.  []   Now I just have to solder it to a protoboard for use outside.

Hi Mark.

 

Where in the top photo is the 10K resistor for the thermistor input?

Do you , perhaps, have a better circuit diagram than the one here in post #32?

Thanks.

 

BTW: I received the SHT31 sensor from Amazon.ca today.

 

https://www.amazon.c...ct_details&th=1

 

Doug

[mlord]

This remains the best circuit diagram.

https://www.cloudyni...-1683688307.jpg

[dlwmacgregor]

OK.

Thanks.

 

Location of 10K resistor?

Is it in that group of wires in the top right of the BB?

[mlord]

No idea. I don't have that setup now. The wiring diagram does show how to connect it correctly though.

EDIT: It must be in amongst the jumpers at top left of the BreadBoard.

Edited by mlord, 23 August 2023 - 07:50 PM.

[mlord]

dlwmacgregor pointed out to me that the old wiring diagram for the PWM and thermistor connection is incorrect now for the HBG3.  So here is the new diagram, with the GPIO pin for channel-0 PWM output changed from 4 to 14:

 

 

For the second channel, if needed, use GPIO 39 for the thermistor, and GPIO 26 for the PWM output.

Edited by mlord, 25 August 2023 - 10:29 AM.

[mlord]

A few people seem to have now discovered that the HBG3 can implement all of the Smart Dew Control functionality of a Celestron 2X Dew Controller for just a few bucks in small parts.  So here is an updated breadboard showing how to do it, for one channel of dew control.

 

Here is the overall picture of EVERYTHING including a 10K thermistor:

 

The large green/black plugs at top right are for 12V power input (5.5/2.1mm DC jack, the right hand one), and 12V PWM power output (RCA jack, the left hand one) to a dew heater.  This will drive _any_ dew heater, so long as the 12V power input has enough amperage capacity.  The Celestron 8" Dew Ring requires a bit over 1.5amps, so a 2-amp supply is good there.  The red PCB that those connect to is a standard IRF520 module off of Amazon.  Cheap.

 

 

The PWM output from the HBG3 is from GPIO14 via the yellow wire, through a diode for protection, and into the SIG input of the IRF520 module.  The blue wire to GPIO34 of the HBG3 is the thermistor input.  It is connected according the the wiring diagram in the post just above, using a 10K resistor to form a voltage divider with the thermistor.

 

The green wire is not needed and can be ignored.  It is connecting the second thermistor input of the HBG3 (GPIO39) to GND, to prevent it from thinking a thermistor is actually plugged in on that channel.

 

The other four colourful wires are the four I2C signals:  black=GND, red=3.3V, orange=SCL, brown-SDA.  The SHT30 ambient sensor (lower left) is wired directly to those four I2C signals.

 

There is a single discrete 10K thermistor (temperature sensor), which is the skinny looking thing at bottom right.  It has a 2.5mm mono plug wired to it, and plugged into a 2.5mm mono jack wired to the breadboard.  Anyone using a Celestron Dew Ring won't need this thermistor, because the Dew Ring has one built-in.

 

 

The OLED display on the HBG3 provides useful information, defaulting to showing Dew Control info when equipped.  The push button on GPIO4 (not shown) can be pushed/held to cause the temperature offset (aka. "Aggression") for the first channel to cycle among all 10 possible values -- currently defaulting to +2.5C above the dew point.

 

 

And of course it is compatible with CPWI and any other apps that know how to manage a Celestron 2X Dew Controller, as well as with the Celestron hand-controllers.

Edited by mlord, 26 August 2023 - 08:45 AM.

[mlord]

Here are the cables needed for each dew heater + thermistor pair:

 

First, the heater cable, which is included with purchase of a Celestron Dew Ring, with RCA Plug at one end and DC 5.5/2.1mm plug at the other:

 

And then a 2.5mm to 2.5mm mono cable for the thermistor connection -- one must source this separately.  Note that a 2.5mm stereo cable (easier to find) will also work -- it doesn't have to be a "mono" cable, and the "signal" is just DC current measured in micro-amperes:

 

Edited by mlord, 26 August 2023 - 08:44 AM.

[pbddict1]

Here's my version of the stand alone:

 

I used a ridiculously large DC-DC buck convertor.. but it was $4 on amazon and has a cool voltmeter in it I can watch battery voltage with (the display can be turned off..good thing... it's bright)

 

I also didn't use any external connectors besides the ones on the end of the wires for the heater and battery. There's some inside the box if I need to replace cables or sensors later..but this way I don't chase parts around in the dark as its all connected,

I'm going to affix it right to my heated dew shield with some velcro.

 

I used a plain thermistor and 3d printed a clip to hold it against the objective retainer ring of my C11 and insulate it a little so it's less affected by ambient temp.

 

I have a CGEM.. so could have used my HBG3... but I like what that is now (small case, simple), and wanted a separate part I could use with anything.

 

Thanks for the code and build info Mlord

[mlord]

I had my rig outside last night, for the first time since September.  It's cold enough here now for Dew to be an issue, and it was last night despite my smart dew controller being used.

 

Last night the air/corrector temperature was around -7C, with a calculated DewPoint around -14C.. yet it fogged up regardless.  Remind me to run a "calibration" cycle on the Dew Heater before going out again.. EDIT: Done!

 

So.. Needs. Work. 

 

I am posting an updated source code for the HomeBrew Gen3 (HBG3) version here.  This is a work-in-progress, but I am hoping it has enough in it now to cope.  It may get trialled again this evening -- just needs the scope outside, I don't actually have to be able to see anything through it!

 

This trial version has much higher "aggression" than before (Celestron's terminology for how pro-active the Dew Heater is).  So higher aggression levels may be able to bridge the gap between the calculated DewPoint, and the actual point at which the corrector lens on the OTA begins fogging up.

 

But the use of the push-button and OLED together has also been enhanced.  Pushing/holding the button while on the OLED screen used to cycle among the available 10 aggression levels.  It still does that, but also now cycles through the manual PWM (heater) settings as well:  0%, 20%, 40%, 60%, 80%, 100%.   So worst case, I can use that to flip it into manual mode and set the PWM percentage.

 

Here's the code, should anyone else want to give it a go:   hbg3.ino.txt   258.15KB   17 downloads

Edited by mlord, 25 November 2023 - 02:11 PM.

[dlwmacgregor]

I wonder how Celestron's Dew Heater Controller compares (not that I'm even remotely thinking of buying one).

[mlord]

I wonder how Celestron's Dew Heater Controller compares (not that I'm even remotely thinking of buying one).

Pretty near identical in parts and operation.  But I don't know how much above the calculated DewPoint they allow before enabling the heat.

 

I actually DO have a Celestron 2X Dew Controller here, which I've never used outside.  Annoyingly noisy thing (fan), and heavy too.  I could hook it up and measure the PWM output in "Auto" mode and see exactly what they do.
 

[mlord]

Here is another pre-release version of the source code for testing.  I expect to release this for real in a day or two:   hbg3.ino.txt   258.65KB   12 downloads

 

This features quite a few improvements to the Smart Dew Heater controls.  It now works with a channel which has no Thermistor -- one can set the PWM percentage manually, either on the OLED with push-button, or through CPWI or a Celestron hand-controller.

 

Changes appear much more quickly on the OLED display now, too.

 

There are other, non Dew related changes that are ready to go.  Just need a bit more confirmation that the Dew stuff is okay now.

 

Cheers