Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Telrad pulser install notes and question

  • Please log in to reply
10 replies to this topic

#1 GunArm

GunArm

    Sputnik

  • -----
  • topic starter
  • Posts: 30
  • Joined: 16 Jul 2018
  • Loc: North Texas

Posted 12 October 2019 - 03:33 PM

I bought the pulser upgrade for my telrad when I bought the telrad.  Honestly I hadn't even used the telrad yet so it was it wasn't a purchase of tested need, more of an impulse buy when picking up a ton of other bits and bobs I did need.

 

I have some comments that might be helpful to someone installing it or thinking of getting it, and then I have a question.

 

Install notes:

The kit comes with a piece of paper with instructions at the top and a drill template on the bottom.  The template is not great.  For one thing the template has an incorrect width of the actual telrad by about 1/8 of an inch, and secondly it has inches in decimal which is just odd.

 

I used a poker and made careful holes in the template targets, lined the telrad up behind the template (as best as possible given the height mismatch) and put a silver sharpie dot through the poked holes onto the telrad.  Then I drilled them out.  The recommended drill size of 9/32 is incorrect as that is not big enough for the threaded part of the knob stem to come through, so you'll have to go a step up from that.

 

Feeding the knob stem from the inside through the hole you drilled is tricky.  Until the tip of the stem goes into the hole slightly there is not enough space diagonally to comfortably wedge the circuit board down into the body of the telard.  You could probably force it but I didn't want to.  (If that sounds confusing you'll understand once you try it).  The very easy solution to this is to put the drill sorta sideways against the top edge of the inner side of the hole and mill out a small chamfer on the top side of the hole.  Once you do this the knob stem can get that millimeter of angled insertion needed for clearance and the thing drops into place very easily.  Obviously the chamfer is not visible from the outside. 

 

Finally, the threaded part of the pot stem is not long enough compared to the thickness of the telrad plastic, even with the pot body flat against the wall, there is no way to get the nut threads to catch on the other side with that tiny washer in between.  I had to ditch the washer, and then use needle nose pliers to push the nut while turning it to get it to catch the tiny bit of threads coming through.  I was able to get a half turn on the nut then, not great, but I think it will hold.

Hope this helps others trying to install this thing.

 

 

Now my question:

This isn't a big deal but I wanted to ask anyway:  The instructions say to use the new knob to cut the power.  The thing is that the second knob isn't as nice as the first lever-knob and my preferred use would be to leave the pulser knob somewhere in the middle and use the original intensity lever-knob to turn it on/off.

The instructions say "The switch on the new control turns the power to the instrument on and off and, to avoid battery drain, must be off when the instrument is not in use".  However I'm not confident they are speaking precisely.  The old knob will still cut power to the illuminator, so it might work equally well as a power switch.  However there *is* new circuitry behind the illuminator now, and I'm wondering if anyone has knowledge of the pulser circuit to know if it would leak current even when the illuminator is switched off?


  • Joe1950 likes this

#2 Joe1950

Joe1950

    Voyager 1

  • *****
  • Posts: 10,445
  • Joined: 22 Aug 2015

Posted 12 October 2019 - 04:50 PM

It depends on how the power lead from the pulsing circuit is wired. If the circuit goes directly to the battery pack, it will stay on, even when the light is off. If it gets power after the original pot/switch, by being connected to the pot switch itself, then the main switch will control both and nothing would stay on.

 

The problem is, looking at the main pot, which is hard to see, I can only see 3 solder contacts. That may mean that the switch is internal, which is not a good thing since you can’t get to it. I think this may be the case since I see only two wires going to the main pot.

 

So I would have to say it’s problematic to get the power off the pot connections. The main pot would be in line with the pulse circuit pot and the interaction would cause it to function oddly, if at all.

 

Eventually, I’m going to add a miniature SPST toggle switch on the side and connected between the battery + and its corresponding wire. I don’t have the pulsed circuit, but I want to leave the brightness lever more or less fixed and just turn the thing on and off.

 

If you did that, you can get your voltage off that switch and turn both on/off at the same time. Without seeing an actual schematic, that may be the best way.

 

Hope this helps.

joe


  • GunArm likes this

#3 GunArm

GunArm

    Sputnik

  • -----
  • topic starter
  • Posts: 30
  • Joined: 16 Jul 2018
  • Loc: North Texas

Posted 14 October 2019 - 12:30 PM

Thanks for the response.  I had been considering a toggle switch also and after considering it I think I'm going to go that route.  Rather than SPST I'll probably throw in a DPDT wired so the 3 positions would be off, pulser, no pulser.


  • Joe1950 likes this

#4 Joe1950

Joe1950

    Voyager 1

  • *****
  • Posts: 10,445
  • Joined: 22 Aug 2015

Posted 14 October 2019 - 01:47 PM

I forgot the pulser. Good idea. I don’t have the pulser on mine. Good option especially for skies where you can see a lot. Here, only bright stuff. 


Edited by Joe1950, 14 October 2019 - 02:01 PM.


#5 JimmyTrom

JimmyTrom

    Explorer 1

  • *****
  • Posts: 61
  • Joined: 15 Aug 2018
  • Loc: Crestwood, KY

Posted 16 October 2019 - 09:35 PM

What magic is in a Telrad LED circuit?

Yesterday I wired a relay ( small) in series wth the power lead from the battery pack.

The relay is powered by a 555 timer circuit with a variable pulse rate controlled

by a pot.  I can hear the relay toggling but the LED in the Telrad stays off.

Even at ~ 1 Hz, still no pulse.  Is it a incandesent bulb?



#6 Joe1950

Joe1950

    Voyager 1

  • *****
  • Posts: 10,445
  • Joined: 22 Aug 2015

Posted 16 October 2019 - 10:02 PM

The light is an LED.

 

This is the pulser circuit with the original 3V source, the variable intensity pot and on/off switch. It uses the 555 timer chip.

 

Your circuit may drop the voltage below the needed LED forward voltage for illumination. Also, did you have the level pot turned high enough?  Something I would forget to do.  crazy.gif

 

Also, depending on the relay, it may cause a voltage drop that limits what the LED sees. A mechanical relay is not needed and may load down the whole works when activated.


Edited by Joe1950, 16 October 2019 - 10:07 PM.

  • airbleeder likes this

#7 TomTTuttle

TomTTuttle

    Explorer 1

  • *****
  • Posts: 57
  • Joined: 16 Apr 2019
  • Loc: Pearl River, LA

Posted 17 October 2019 - 10:34 AM

I must be looking at different instructions.  I saw a diagram but I didn't take it as a 1:1 scale template, but should that the holes are 1/4 and 1/2 inch from end and .7" from the inside bottom. An outside measurement would have been better.  The decimal doesn't bother me - my calipers do both. So hole = 0.7 + (outside height - inside height).  A true template would have been better and should have been easy for them.

 

But these instructions have 5/16" or 8mm for the larger hole.  These work out to 0.3125" or 0.3149" as opposed to 9/32 being 0.28125".  I wonder when (and why?) they changed it.


  • Joe1950 likes this

#8 Joe1950

Joe1950

    Voyager 1

  • *****
  • Posts: 10,445
  • Joined: 22 Aug 2015

Posted 17 October 2019 - 10:39 AM

Maybe they are being made elsewhere, as with most things. Don’t know.



#9 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,474
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 17 October 2019 - 01:05 PM

 Many years ago I design and sold a Telrad pulsing circuit. It is used a LM3909 instead of 555. The great thing about the LM3909 is that it uses a charge pump so it will drain all of the power out of a set of AA batteries. Batteries that test dead would still flash the LED brightly. It also worked on the original 3 volt  AA battery system and used the original switch and brightness control on the Telrad. My  circuit used a miniature pot  on the circuit board to set the pulse rate and the board was 1'"square so it would fit inside the battery compartment of the Telrad. I had  batteries last 5 years in my Telrad even when I have forgot to turn the unit off. 

   Here is a link to the data sheet. Note it states that it will flash an LED for 6 months continuously on a pair of AA batteries..  http://solarbotics.n...eets/LM3909.pdf     You can still  get LM3909s on Ebay.

 

                  - Dave 


Edited by DAVIDG, 17 October 2019 - 01:24 PM.

  • Joe1950 and TomTTuttle like this

#10 MikeMiller

MikeMiller

    Viking 1

  • -----
  • Posts: 858
  • Joined: 22 Jul 2014
  • Loc: Pittsburgh, PA, USA

Posted 31 October 2019 - 09:43 AM

I always switch them both off. The blinker knob is less likely to get bumped on than the original lever when it is being stored.

 

But if it is during an observing session, it doesn't matter. The thing uses so little power that I occasionally leave it switched on for a couple of weeks at a time and the batteries are still good.



#11 wrvond

wrvond

    Surveyor 1

  • *****
  • Posts: 1,895
  • Joined: 25 Sep 2014
  • Loc: West Virginia

Posted 10 November 2019 - 08:30 PM

I was considering the pulser but now think it is more trouble than it is worth.

You guys just saved me a bit of money! waytogo.gif




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics