Spin Semiconductor

I wondered when setting up the input levels to the FV-1 if the clipping LED conducts what is the likelihood of damage to the FV-1 chip.
I am trying to get as close to the 3.3v input as possible without actually clipping the internal ADC but when using different instruments one can easily drive the level too much while the others will give a low signal. Adding level control helps but this also means it can be left high and when using a high output pickup easily illuminate the clipping LED.

Also can pin 5 sink enough current to fit 2 LEDS. ie, one SMD Led on the underside of the PCB next to an internal gain trimmer for set up of max level along with one on the front panel for visual display.

ice-nine wrote:I wondered when setting up the input levels to the FV-1 if the clipping LED conducts what is the likelihood of damage to the FV-1 chip.

I'm not clear on what you mean by this, the clip LED will turn on at about 6db below clipping if I remember correctly.

ice-nine wrote:Also can pin 5 sink enough current to fit 2 LEDS. ie, one SMD Led on the underside of the PCB next to an internal gain trimmer for set up of max level along with one on the front panel for visual display.

If you run them in series it should be OK since the current will be the same but you may need to adjust the current limit resistor value slightly.

frank wrote:

ice-nine wrote:I wondered when setting up the input levels to the FV-1 if the clipping LED conducts what is the likelihood of damage to the FV-1 chip.

I'm not clear on what you mean by this, the clip LED will turn on at about 6db below clipping if I remember correctly.

ice-nine wrote:Also can pin 5 sink enough current to fit 2 LEDS. ie, one SMD Led on the underside of the PCB next to an internal gain trimmer for set up of max level along with one on the front panel for visual display.

If you run them in series it should be OK since the current will be the same but you may need to adjust the current limit resistor value slightly.

I was meaning if the clip LED turns on quite a lot is it likely that the input of the FV-1(ADC) may get damaged due to a high input signal level.

Second point was answered well about 2 leds.
Thanks

OK, got it. If you run it fully on for a very long time it might but for just for a few minutes while adjusting levels should be fine.

frank wrote:If you run them in series it should be OK since the current will be the same but you may need to adjust the current limit resistor value slightly.

You probably will not be able to run them in series. The forward voltage of two LEDs in series will be 3.6v or more, and there is only 3.3v powering the FV-1, so they will not turn on.

Not absolute, and it is possible to get two low Vf LEDs that will light up but you will have to pick the specific components. The current limit resistor will have to be quite low, say 10 or 22 ohms. (This is not my preferred solution.)

I suggest that you just use two LEDs and two dropping resistors in parallel and it should work fine. Each resistor needs to be 220 ohms or more. The LEDs will be plenty bright and you will not exceed the current draw shown on the datasheet, which is about 14 ma. A 470 ohm resistor on each is even better and with efficient LEDs it will be bright enough (about 3ma each).

regards, Jack

amz-fx wrote:

frank wrote:If you run them in series it should be OK since the current will be the same but you may need to adjust the current limit resistor value slightly.

You probably will not be able to run them in series. The forward voltage of two LEDs in series will be 3.6v or more, and there is only 3.3v powering the FV-1, so they will not turn on.

Not absolute, and it is possible to get two low Vf LEDs that will light up but you will have to pick the specific components. The current limit resistor will have to be quite low, say 10 or 22 ohms. (This is not my preferred solution.)

I suggest that you just use two LEDs and two dropping resistors in parallel and it should work fine. Each resistor needs to be 220 ohms or more. The LEDs will be plenty bright and you will not exceed the current draw shown on the datasheet, which is about 14 ma. A 470 ohm resistor on each is even better and with efficient LEDs it will be bright enough (about 3ma each).

regards, Jack

Thanks for the info Jack, I missed the 14ma current draw in the datasheet. Running the LED's in parallel with their own current limiting resistors was my preferred way of doing it.

The 14ma current limit is not on the datasheet, it is just what it works out to be with the 100 ohm resistor shown in the same schematic. Most pins are 20ma limit so I suspect that is the absolute max.

regards, Jack