LM3914: Can LM3914 be used as an exclamation point and an alarm flasher simultaneously and turned on/off remotely?

Hi,

I have notified our expert regarding this topic. Please expect a response by 11/14/18.

Thanks,
Aaron

Aaron Goodson said:

Hi,

I have notified our expert regarding this topic. Please expect a response by 11/14/18.

Thanks,
Aaron

Thanks for noticing my question. I'm still dumbfounded by this riddle. Still not sure if it can be achieved but I'll be looking forward an expert advise which can guide me on what to do.

Hi Chris,
I reviewed the datasheet for this device and it seems that mode can be changed between dot and bar by connecting the mode pin to either V+ or leaving it open. You can use a mosfet switch and logic level signal to control the switch. Mode pin will be connected to V+ when this switch is closed and no connect when this switch is open. As for remotely disabling the LM3914, I don't see any pin that can used for this purpose. You may consider using a load switch such TPS22919 or similar or a power mosfet switch to disconnect power to LM3914 to disable it.
I hope this is helpful.
Kind Regards,
Liaqat

Liaqat Khan said:

Hi Chris,
I reviewed the datasheet for this device and it seems that mode can be changed between dot and bar by connecting the mode pin to either V+ or leaving it open. You can use a mosfet switch and logic level signal to control the switch. Mode pin will be connected to V+ when this switch is closed and no connect when this switch is open. As for remotely disabling the LM3914, I don't see any pin that can used for this purpose. You may consider using a load switch such TPS22919 or similar or a power mosfet switch to disconnect power to LM3914 to disable it.
I hope this is helpful.
Kind Regards,
Liaqat

Dear Liaqat I'm aware that LM3914 can be changed between dot and bar. However that is not my concern. The problem is if there is a way to make the driver to work as a bar display with alarm flasher seen in figure 20 (see datasheet for reference) AND "exclamation point" display as seen in figure 18. Both examples appears separately and there is no hint for telling if they can be combined. Therefore my question addresses this. Can THOSE modes be combined?. Again, I'm not implying to change between states (supposing you say to use a mosfet switch to toggle from one mode to another). It would also help if you could explain me what it is intended to mean by "exclamation point", so as the last led from the rest is keep blinking while the others below from it are turned on?. If so perhaps I'm imagining that when the signal reaches the last led it could trigger some sort of a switch to shift at that moment from that mode to the one seen in figure 20 (alarm flasher) therefore giving a result of blending both modes as it is in my question. But I don't know how to make that wiring or what would be needed to do so. So this part I need help.

The rest of the answer referring to use a mosfet switch for remotely powering on and off would be improved if there is some schematic on how would be used with LM3914. Can you add one? I did taken a look at the TPS22919 as you mentioned but there isn't exactly much aid in how to use it for powering on other chips rather than a load resistor (seen in figure 5). I hope you can help me with these questions. Thanks in advance.

Hello Chris,

My apology about the delay in response but I unsuccessfully tried to get hold of an EVM for this device so that I can try few experiments to see how we can achieve the so called exclamation point and alarm modes simultaneously but, unfortunately, this is an older device and I was not able to get hold of an EVM.

I don't exactly know what is meant by the exclamation point but looking at the circuit in figure 18, it seems to work like this: Input signal would gradually charge 0.02uF capacitor with a time constant of 0.2ms. The voltage at capacitor would rise faster initially and slow down as capacitor approaches full charge to input signal level. This would visually have the effect of lower brightness for the first dot and higher brightness for successively higher dots with highest dot having the most brightness as that dot will stay lit the longest.   So the effect would be like an exclamation mark! to human eye. This effect would repeat every 1ms (1KHz pulse that discharges the capacitor). Hopefully my description makes sense.

As of now, I don't understand how the two effects of "exclamation point" and "alarm flasher" can be be combined. If I am able to get hold of device, I will experiment in my spare time to see if something like that can be done. I hope my response is somewhat helpful.

Kind Regards,

Liaqat

Thanks for taking note of my earlier comments about this device. Hopefully you did replied. After trying to look into LM3914 datasheet it looks that it does not seem to support to use an alarm flasher and an exclamation point indicator both at the same time as you pointed out. I must note that I do not have enough expertise to experiment on this IC by my own therefore I'm asking for assistance.

What I meant as an exclamation point display is shown in figure 18, page 14 from Rev. B from TI documentation for LM3914. In the bottom reads "LEDs light up as illustrated with the upper lit LED indicating the actual input voltage. The display appears to increase resolution and provides an analog indication of overange". The description which you mentioned about how the capacitor acts as a time constant I understood but this was not exactly what I intended to ask.

What I meant about "exclamation point" and "alarm flasher" was to know if what it is suggested in the example shown figure 18 and in figure 20. "Bar display with alarm flasher" (see page 15 on Rev B. documentation for LM3914) can be combined?. In other words can those examples shown be combined?. I.e, let's suppose a gradual increase from 0 to +6V in the input whose threshold is +5V would make overrange making full scale to flash. But before that an "exclamation point" would be in place, in other words before that threshold is attained the last led to blink as it is described in figure 18.

I'm not sure if my reply did made my question more clear, but if you have doubt I can rephrase my question again. Anyways I look forward to know if this can be achieved. I understand that this chip is an older device therefore this is why I'm asking such question whether if it can yield such result. Again, hope I can read some updates from the question I posted.