Remote controlled CCTV surveillance system - Arduino based

[Gina]

Managed to tidy up the diagram a bit.

[Gina]

This design will be suitable for any application using stepper motors such as focusers etc.  You can control two at once with this.

Where the supply is 5v rather than 12v this can be used with 5v steppers as shown below.

[pete_l]

Managed to tidy up the diagram a bit.

SmartDraw CCT Drawing 06.JPG

Zener's upside down:

[Gina]

OOOPS   So it is - you're right - silly me

[tekkydave]

Zener's upside down:

I thought something looked 'not quite right' when I was looking yesterday but couldn't put my finger on it

I notice you have the common on the motors at +12v so the coils are energized by driving the other end low. Nothing wrong with that, is it a consequence of the driving circuit only operating in open-drain mode. On my focuser the stepper driver is fed from an arduino digital i/o pin which it says can source or sink up to 40mA so it ought to work either way. The arduino output stage must be more sophisticated than the DS2408. It is targeted at 'experimenters' so it probably needs to be

[Gina]

I thought something looked 'not quite right' when I was looking yesterday but couldn't put my finger on it

I notice you have the common on the motors at +12v so the coils are energized by driving the other end low. Nothing wrong with that, is it a consequence of the driving circuit only operating in open-drain mode. On my focuser the stepper driver is fed from an arduino digital i/o pin which it says can source or sink up to 40mA so it ought to work either way. The arduino output stage must be more sophisticated than the DS2408. It is targeted at 'experimenters' so it probably needs to be

Glad someone noticed the Zener polarity   Hopefully before anyone copied my design and built it

The DS2408 has open drain outputs without pull-up resistors so can only sink current.  The Arduino has totem pole outputs so can either source or sink current.  The TC4469EPD driver chip also has totem pole outputs and can either source or sink current (a lot more than the Arduino).  So I could have the common line of the steppers grounded instead of connected to the +12v line.  The only difference would be the state of the logic.  The TC4469EPD has both inverting and non-inverting inputs so either logic state can be used by suitable wiring.

As for driving stepper motors, the 28BYJ-48 would overload Arduino outputs if connected directly.  The 5v version takes 100mA (50ohm coils). the 12v version only takes 40mA but needs 12v, of course, and the Arduino gives only 5v.  It would have to be a lower power stepper motor tro work directly off an Arduino.

I have used the Arduino to operate relays but you have to watch the total current - you can't draw 40mA from several digital outputs at the same time, there is a limit on the total output curent as well as for individual outputs.

[Gina]

I have ordered the stepper drivers and the resistor networks and should have everything needed for testing Wednesday   So that should be the pan and tilt electronics sorted out.  Next I need to work out how I'm going to select the video for the array of cameras.

Two possibilities I can see ATM.  The original idea of multiple relays or using an analogue signal selector chip feeding into a video amplifier.  I already have the relays (if I can find them) as I had bought the components for the earlier system.

Not quite sure yet how many cameras I want to use.  I used to have 10 cameras to cover the whole area but with pan & tilt I think I could manage with fewer.  If 8 or fewer I could use a DS2408 and two TC4469EPD drivers to drive relays.  Thinking about it I reckon I could use fewer since the relays are two pole.

[ncjunk]

You can get a block of 8 relays cheap from china and you can supply a separate voltage to the relay circuit. I found that without external power I could command 6 relays. Theres still a nominal current draw on each output when externally powered but I can't remember what it is.

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[Gina]

Thanks Neil

[ncjunk]

I would put more details but I keep getting jumped on by my 3 and 5 year olds if I am trying to do anying thats more than 2 mins!

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[tekkydave]

Thanks for the info. My focuser uses the ULN2003 chip as per your initial diagram but on 9V. The arduino should only be sourcing a few mA I think but havent measured it.

[Gina]

:)

Using 4 DPDT relays to select one of eight video feeds.  Two relay coils connected together to emulate a 4PDT relay.

The ABC represent binary code lines.

ie.  ABC   n

      000 = 0

      001 = 1

      010 = 2

      011 = 3

      100 = 4

      101 = 5

      110 = 6

      111 = 7

[Gina]

Thanks for the info. My focuser uses the ULN2003 chip as per your initial diagram but on 9V. The arduino should only be sourcing a few mA I think but havent measured it.

Yes, the input current to each input of the ULN2003A is <1.35mA in the 1 state so absolutely no problem.  I'm using ULN2003As with Arduinos for my focusers.

[Gina]

I now have the DS2408s, the little boards to mount them on and the stepper motor driver chips.

[Gina]

I guess that by the time I get back to this I shall have well and truly lost the components I have carefully collected   I need to get all my stuff sorted out into appropriate labelled containers.   I have done some tidying up and sorting out but it's a long job

I'm currently reviewing all my numerous projects hence the post.

[Gina]

Back here reading what I was doing on this project as I have a plan to use DS2408 chips with SOIC16 to DIP PCBs and a little voice in the back of my head said "Didn't you get SMD to DIP PCBs for the CCTV system?" so I looked up this thread   Took a while to find it.

My last comment on this project was "I guess that by the time I get back to this I shall have well and truly lost the components I have carefully collected :(" and guess what?  Yep - 'tis true - I don't know where they are   I have already ordered a couple of DS2408s which have already arrived and a couple of the adapter boards which I'm waiting for, for my latest project.  This just goes to show that I really MUST sort my stuff out!!!

[Gina]

Found most of the bits   10x DS2408, 10x SOIC16 to DIP PCBs, 8x TC4469 quad MOSFET drivers, 9x SIL resistor networks with 8 10K resistors (one end common) in each chip.