symmetal

Peter, Just noticed re the pull up on the hall effect switch. Connecting the resistor between the hall effect power and its output would pull the output to 12V when the switch is 'off'. This would mean the VM110 digital i/p gets pulled up to 12V too which could cause problems as the board is 5V powered. If you do want an external pull up resistor it has to go between the switch output and +5V. Omitting the external pull up is the best option as the board is almost bound to have one on the digital inputs. I didn't reply before, but you mentioned if the 3 diodes were necessary. The diode between Dig Out2 and Dig In4 on the VM110 is there to protect Dig In4 from rising above 5V if Dig Out2 is pulled higher than 5V by the relay board. Whether the relay board IN- inputs rise to 12V or 5V when the relay is off I don't know but it doesn't matter as the diode protects Dig In2 if it's 12V. The diode going to relay board NO4 is actually reverse connected across the motor terminals if you follow the wiring. This is there to protect any circuitry from the back emf voltage spikes generated by the motor when it turns off. Not always necessary but it's good practice to have one. The diode going to relay board DC+ is just circuit protection from accidentally connecting the lead acid battery the wrong way round. None of the diodes are passing much current so standard 1N4001 diodes or similar would do. Alan

Peter, Yes, testing the hall effect switch on it's own and not connected to anything the pull up is required to measure an output change. Hope it all works OK when you try it out after the board has arrived. I notice you haven't shown a fuse in the +12V line from the lead acid battery. If there is a wiring error or a fault, and the battery gets shorted you run the risk of something smoking and getting burnt. Lead acids can deliver very high currents, even a modest capacity one like you're using. Depending on the power of your dome motor its start up surge may blow a 10A quick blow fuse. A 10A antisurge fuse would be more robust, but it may need a 15A or similar fuse to stop it occasionally blowing on start up. A 15 or 20A fuse would be better than no fuse at all. Alan

Peter, You're latest drawing and explanation is clearer now as you just want the one 5V USB cable coming from the powerbank. Your drawing looks like it will work OK as you want it to. I'm not sure what the 10k resistor next to the hall effect is for as it's effectively just across the 12V lead acid battery. If it's to be used as a pull up for the hall effect switching signal it need to go between the brown and black wires of the switch. To check if a pull up is actually needed just power the VM110 via its USB socket and with no connection to a digital input pin measure the voltage on the pin with your multimeter. If it reads 5V as I'm sure it will, then the board has a pull up on each input anyway so an external one isn't necessary. Also there is a connection just going between Dig Out3 to Dig In3. What purpose does this serve? Alan

Peter, It was only after your last post that I realised you were using the Powerbank as well as the 7Ah lead acid. As the VM110 only requires about 70mA (from the manual) it can be easily powered from one raspberry pi USB connection. USB2 should be able to supply 500mA per output, and though the Raspberry Pi isn't capable of supplying that much current, I'm sure the 70mA will be no problem, so a clamp connection is not needed. A second USB output from the Pi could be used to power the rotary encoder as that needs around 20mA I think. You'll need to chop one end of the USB cable to get access to the 5V wires for the encoder power or use a USB breakout board if they exist. Where are you getting the 5V to power the Raspberry Pi from. The powerbank 5V output? Rather than using a second USB lead from the Pi or a buck converter to power the encoder could it not be connected to the 5V powering the Pi. If you want the 7Ah lead acid to power only the motor, the relay board 12V DC+/- connections (which power the relay coils) could then come from the Powerbank 12V output which could also power the hall effect switch. It's best to connect the negative (Gnd) terminals of the powerbank and 7Ah lead acid together to avoid floating voltages though if the lead acid only goes to the relay board contacts to power the motor it's not strictly necessary as they are isolated from the rest of your circuitry. Alan

The Clamp connection is a voltage input (5-30V) to power the VM110 if you don't have a USB cable connected. At least that's how I see it. The VM110 data sheet shows it as a input so I doubt you could use it as an output to power something else. The VM110 draws 70mA which the USB connection should be able to supply without problems but you may as well connect the clamp input to your 12V battery supply as it's there. My solution would be to connect your +12V battery supply to the clamp input and the hall effect switch +V terminal. Then use a 5V output buck converter also powered from the 12V battery and use the buck converter 5V output to power the rotary encoder. This way everything stays powered whether or not the Raspberry Pi USB is connected or not. You haven't mentioned how the Raspberry Pi is powered. It could be powered from the buck converter 5V output to keep everything simple if you wish. Reading your above post again will you be using the 7Ah lead acid as well as the power bank to power the project. If so, you could use the power bank 5V out to power the rotary encoder (and possibly the Pi) but a 5V buck converter off the 12V would be a neater solution I would think. Alan

The Velleman Clamp input can be from 5V to 30V. I assume this feeds an on board regulator and that the board itself only uses 5V. (Not sure why it's called Clamp and not +V In). I assume also the Clamp power is needed if there is no USB connection otherwise the 70mA the board uses could come via the USB. Hugh could confirm this. The VM110N data sheet is not very clear on this. The digital inputs are all switches to Gnd and the digital outputs are all open collector so the board doesn't need to supply any real power to anything connected to it. As you say you'll need 5V to power the rotary encoder so a buck converter or a 7805 regulator powered from the 12V would do. The encoder only needs a few mA. You could connect the clamp input to the 12V or the 5V as either would work for the Velleman board. The Hall effect switch brown (+ve) just needs to go to any 12V connection available, so not necessarily the Clamp voltage. The Blue (-ve) to Gnd and the Black ( signal) to Dig In1 as you stated. When you put the magnet close to the sensor the open collector output transistor will switch on so pulling the output to Gnd. You would then measure about 12V across the pull up resistor you've connected, if you're powering the Hall effect from 12V. When you move the magnet away the output transistor turns off so no current flows through the pull up resistor so you measure no volts across it. As the Velleman digital inputs are just looking for a switch to ground I'm pretty sure they will have their own pull up resistor on the board inputs. Alan

Hi Peter, There are a couple of things that need changing on your diagram. The relay board needs to be permanently powered by the 12V. The DC- currently goes to Dig Out2 so the board is only powered when Dig Out2 goes low. If the board isn't powered then your SPST relay 4 can't be operated. This didn't matter on the ELK-924 board as it didn't affect the ELK-912 SPST relay power. So Dig Out2 should just go to the IN1- and IN2- connections and not DC-, and DC- should be connected to Gnd. Dig Out1 switched the SPST relay on the ELK-912 board by grounding the coil -. On your new diagram you've shown it going to DC- and so connecting DigOut1 to DigOut2 which isn't what you want. Dig Out 1 needs to go to IN4- only, to enable the SPST relay 4 to be switched. Currently there is nothing switching relay 4. This is also why the relay board needs to be permanently powered, to allow relay 4 to be switched independently from relays 1 and 2. I'm surprised that a pull up resistor is needed with the hall effect switch when connected as shown, as the Dig In2 input should have its own pull up resistor. The current reed switch just grounds Dig In2, and no pull up resistor is shown, which is all that happens when you connect the hall effect switch output to Dig In2 instead. There's no harm in adding another pull up resistor as long as it pulls up to the logic voltage the Velleman board uses. The hall effect switch can be powered from 5V or 12V or any voltage within its specified ratings and won't have any effect on its operation. This is assuming you have one with an open collector output, which most are. This is a benefit as it isolates the output switching from the input power. Being open collector it would need a pull up resistor somewhere but this can be pulled up to any positive voltage which suits the circuit it's connected to and need not be the same as the hall effect switch power voltage. Alan

The board that Hugh and Steve suggest has four independent SPST relays so one relay can be your SPST relay, and two relays with their trigger inputs connected together will become your DPDT relay. A hall effect switch needs to be powered all the time to function, via the Vcc and Ground pins, while the Output pin is usually an open collector transistor (or open drain mosfet) like this If the reed switch you want to replace with the hall effect switch is the Home Sensor switch then you just connect the output pin to Dig In2, Vcc pin to +12V and Ground pin to Gnd. Make sure you use a hall effect switch that can operate from 12V as some are 10V max working. If the reed switch doesn't have one terminal connected to ground then it's not so simple to swap it with a hall effect switch. Alan

For wiring without needing soldering you can use these 12V 10A DPDT octal base relays with Relay socket. You can just use one set of contacts for the SPDT relay, so you only need one relay type. You only need to then get 1 spare relay which will fit either socket. The ELK-924 only needs 1mA to operate the relays as it has on board driver transistors while the RS relay needs 100mA. If the Velleman P8055 which provides a switched ground to operate the relays can't sink the relay coils 100mA, an interface driver transistor will need to be incorporated which makes the design slightly more involved, but can easily be built on a bit of veroboard or similar. The Dig Out1 can operate the SPDT relay directly so can sink enough current. If the Dig Out2 is similar you should be OK without a transistor interface. Alan

Good that you've narrowed it down to the motor. If you're able to disassemble it it's worth having a look inside. Alan

If the probes aren't thin enough just wrap a bit of wire round the probe tips and poke the wire into the connector. If it's still powered make sure you don't short anything out. A motor that has burned out due to over stressing it will usually have a distinctive smell which will linger for days after. If your dec motor doesn't smell 'odd' it may be OK though that doesn't rule out a wire connection failing internally. Hope the replacement if needed isn't too expensive. Alan

The two wires going to the motor body look as if they are soldered to tags on the motor and coverered with heatshrink so no they won't pull off. The wires going to the connector at the end of the motor look like low profile plug and socket which should pull apart. Apply a little leverage to one end with a small screwdriver to see if it moves and then apply a little leverage to the other end. Don't pull on the wires themselves with any significant force as you may just end up pulling the wires off. As you say a multimeter is a very useful tool in this situation. Good luck. Alan

Yes, as Tomatobro said, your connector swap indicates the problem is with the Dec motor or the cable connecting it to the board. Check that the individual pins on the Dec motor connector are fully pushed into the socket housing. Alan

Here's mine. If only the clouds would behave themselves. Alan

The two controllers you've mentioned are really very overpriced, along with the Astrozap for what's actually in them and you're paying for a brand name in my opinion. The Hitecastro is a 4 port with the same functionality and 4 outputs instead of just 2 at £74. The Lynx-astro is also a 4 port at £99 but also has PC control of power settings via a USB connector which may be useful. The 2 port Lynx Astro controller at £69 also has PC control but the two outputs are not individually controllable with one setting affecting both. A much cheaper alternative is to buy a couple of PWM controllers like these. You'll need to build them into a suitable box but if you're diy minded it's the way to go. These are only 2A per channel but is fine for most dew straps. You can get higher current versions if you want. Alan

Thanks for the comparative shots Dave. The RedCat comes a poor third. Same direction coma over the whole image is what I get with the majority of my camera lenses, especially the Samyang 14mm. Are you going to wait to see if Es' Reid can fix them. Taking a chance on a replacement maybe too risky. I've PM'd Steve at FLO to see if he knows whether Es' has managed to fix my first RedCat. If so, I think WO should reimburse FLO for the costs in having to send them to Es'. The Canon 300mm looks good but as I also have a WOZS61 the difference in focal length is not that great to warrant getting one I think. I'll probably look at a 135mm or so lens to fill the gap. . Alan

No that doesn't look good Dave. On my 2 Cats the central stars were very good. On your reduced scale first image there is visible coma too, on the right hand side. I haven't heard any feedback results yet after my RedCats second visit to Es' Reid. Alan

At least it shows that a properly aligned RedCat can produce very good results which is encouraging. Was this an off the shelf scope or one that was given a more rigorous alignment session for promotional purposes. Was the sensor size mentioned, and was the image cropped? ? Alan

Thanks Dave, hope your RedCat's a good 'un. Alan

Thanks for the link R3tro. After sitting though the 1 hour video he didn't compare any images of the two lenses, never mind star images, which should be the main point really. Many camera lenses don't produce good star shapes when fully open particularly at the edges. I 'll have to search for sample star images taken with the Canon 300mm. I've tried astro pictures taken with my Canon L 100-400 zoom and the star shapes were awful towards the edges at all zoom positions and unusable really. I know a zoom is worse than a fixed lens in that respect. My Samyang 14mm and Sigma 50mm fixed lenses are also bad on stars all over the field. The only lens I have that gives good star shapes into the corners is the Canon 40mm 'pancake' lens. The bird image only shows the centre as he says so tells you nothing really except that a Petzval lens is sharp in the centre. I'm not sure how the WO design corrects the inherent field curvature. The Petzval front doublet causes coma. The second doublet corrects the coma (in theory) but introduces field curvature, causing the rapid fall off in focus towards the edges. In the two Redcats (one white) I've tried the flatness looks pretty good, but the coma correction is off. If Es' Reid can fix that I'd be happy with the Redcat. I'd agree that the RedCat is really no good for wildlife photography as the focuser is far to stiff for quick adjustment and needs two hands on the focuser to make small adjustments. Pre-focusing on a certain position and hoping the subject appears in the right spot is the only way. The focus tension ring isn't needed really as the no tension stiffness would prevent the lens moving by itself anyway. One handed focusing always causes it to overshoot if you try to nudge it, as you need to apply so much force that a second hand to 'brake' the focuser is required (when using the bahtinov mask for fine focus). Alan

Thanks for the update Steve. Alan

Have you had a chance to try it out yet Steve? It looked clear over Exeter yesterday. Alan

This notice from the US Naval Observatory explains the cause of the problem (bottom of notice) with an extract below. The week counter was only 10 bits so rolls over every 1024 weeks. So it can affect many older GPS receivers and not just Celestron. Alan

Hi Tim, About 5 posts after the one you quoted I did do a test with a blue filter and focus. I found the focus was more critical using the bahtinov mask in the corner rather than a 'third' but having achieved the central spike in the corner, I checked over the whole image moving the bright star around and focus was still very good with the mask over the whole image. The CCDI analysis of my first test focusing on a third, and the second test focusing in the corner were almost identical so I think the image field with the Redcat is actually pretty flat. Coma is therefore the main problem, and it would seem that the bahtinov spikes are not affected by coma, and the coma isn't really changed by focus. Here's a longer exposure of 120s using the blue filter with the imaging train orientation like the last one of my L images above, which gave the best 'flat' analysis for L. As you can see the blue result is worse than L which is to be expected. View the image at full size to see it more clearly. Three of the corners showed significant coma with the fourth corner slight coma. Alan

That's good news that Es adjusted it out Steve. I suppose the definition of 'a little' is in the eye of the beholder. A full frame sensor would show it worse than the 1600 I'd have thought. Hope your assessment goes well. If it does there's a WhiteCat here that I think would enjoy a visit to Es. Alan