Paris Headamp Low Voltage Indicator

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stereodave

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Paris Headamp Low Voltage Indicator
« on: 27 Mar 2011, 11:15 am »
I'm very impressed with the performance of my Paris Headamp but I have been caught out several times when the SLA battery has lost charge and the signal has broken up. So what is the minimum acceptable voltage and how can I install an indication LED that only lights up when the voltage is too low? I'm sure this is possible but can it be done without programming an IC.

AKSA

Re: Paris Headamp Low Voltage Indicator
« Reply #1 on: 27 Mar 2011, 09:49 pm »
Hi Dave,

Thanks for the post, and welcome to the forum!

I would say no less than 8V on the SLA.

Simplest way to do it is attach an 8.2V zener cathode (half watt or even 100mW is fine) on the positive supply, wire a 470R resistor to the anode end, then attach the other end of this resistor to the anode of a green LED (3mm or 5mm to taste, anode is longest lead).  Then connect cathode, shortest lead of LED, to ground.

Use this as your indicator LED when you switch on your Paris headamp.

If the voltage of the SLA falls to 10V from the nominal 12V, the intensity of the LED will about halve.  At 8.2V, the LED will actually go out, even if switched on, indicating dangerously low charge.

This will be a useful visual indicator, and will give you a tracking method viewed from a distance.

Hope this helps, happy listening!!

BTW, a German hobbyist measured the Paris headamp and found its noise levels at -143dBA.  This is astonishingly low, the lowest he measured in a number of headamps he tested!

Cheers,

Hugh

stereodave

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Re: Paris Headamp Low Voltage Indicator
« Reply #2 on: 28 Mar 2011, 07:42 am »
Thanks Hugh,

Sounds straight forward enough. Much better than needing a multimeter in the lounge room.

andyr

Re: Paris Headamp Low Voltage Indicator
« Reply #3 on: 3 Apr 2011, 06:35 am »

I'm very impressed with the performance of my Paris Headamp but I have been caught out several times when the SLA battery has lost charge and the signal has broken up. So what is the minimum acceptable voltage and how can I install an indication LED that only lights up when the voltage is too low? I'm sure this is possible but can it be done without programming an IC.


Can I suggest you modify your build slightly, Dave.  :)

I built my Paris with a switch on the front and a pair of charging banana-sockets ('+'/'gnd') on the back.
When the switch is down, the battery is connected to the Paris board (and the 'On' LED) and music flows.
When the switch is up, the battery is instead connected to the charge sockets.

I normally turn Paris on a couple of hours before I am going to do some listening (to ensure she's "warmed up") and then put the switch to "charge" when I've finished for the evening.  That way, next time I want to listen ... I know the battery is fully charged.  :)

Regards,

Andy

ginger

Re: Paris Headamp Low Voltage Indicator
« Reply #4 on: 11 Apr 2011, 12:07 am »
Trying to indicate low battery voltage is always "fraught" - at some level of "lowness" it is going to stop working.

Better to indicate battery OK.

OK, we want a circuit that conducts current (for a green OK led) when voltage is above a predetermined level.
That sounds like a shunt regulator IC to me - in fact look at the application notes on a TL431 shunt regulator IC (or a TLV431) and you will see a battery monitor circuit.

A 2 resistor divider to set the gate voltage. When the gate voltage is above 2.5V the chip conducts. A LED and a current limit resistor in the conduction path.

When battery volts drop to such a level that the gate voltage is below 2.5V the IC does'nt conduct and the LED doesn't come on.

Cheers,
Ian

ginger

Re: Paris Headamp Low Voltage Indicator
« Reply #5 on: 11 Apr 2011, 01:07 am »
If you ONLY want the Volts > Vmin indication then ditch R3 and R4 and the 2nd (RHS) TLV431




Extract from the ON Semiconductor TLV431 Datasheeet.

ASIDE: Just finished design and build of a fast LED pulser for testing our laser receivers. The little 3mm Green LED is being hit with 5ns 20A pulses at 1500Hz  - it seems quite happy despite the 20A being about 500 times their continuous current rating.

Cheers,
Ian
« Last Edit: 14 Apr 2011, 03:38 am by ginger »