Re: Re[2]: LF: Automatic variometer circuit

[Andy Talbot <andy.g4jnt@gmail.com>]

Actually, looking again at the circuit again, it is not necessary to use an opamp in that position to define the mid rail for the comparator reference.    Just two equal; value resistors and one electrolytic decoupling the junction to ground (Definitely not two caps to top and bottom in the original configuration shown ... think about it...)  

You only need an opamp to define a stiff mid rail voltage where there is likely to be any significant current draw.  Or many stages need to be referenced to it - such as a multi stage filter.    For single stage configurations, just two resistors and a bit of decoupling is enough

Andy  G4JNT

On 31 October 2015 at 13:20, Chris Wilson <chris@chriswilson.tv> wrote:

Hello Stefan,

Friday, October 30, 2015

Thanks  for the detailed info, and thanks to Andy `GNT for the info re
the  caps. I will order the I/C's for this circuit, and I have ordered
a  2  RPM  reduction  drive motor and some micro switches for the limit
switches, so will be giving this a go! Much appreciated.


> Hi Chris,

> My motor draws about 200 mA at 12V. It has about 1 round per 3 seconds i
> estimate. Costs are below 10 EUR. You will find something on ebay for
> example.
> I use end-switches in the construction BTW, see
> https://dl.dropboxusercontent.com/u/19882028/LF/variometer%20end%20switches.jpg
> just to prevent the wind-up of the cable, antenna wire, coax (would
> sound like "crrrrrkftftftftftplingftftftftbuffftftftft...")

> 73, Stefan








--
Best regards,
 Chris                            mailto:chris@chriswilson.tv