| Electronics > Beginners |
| How to use LM3914 bar graph to indicate 7S Li-ion |
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| StillTrying:
Just removed the lower resistor R7 and connected R5 between BAT and pin 5. That won't work because Vsig = Vbat = V+ = RHI and Page 7, Common-Mode Limits says the inputs can't go within 1.4V of V+. www.ti.com/lit/ds/symlink/lm3914.pdf |
| anishkgt:
The LM3914 is set up for Rlo =3V and Rhi at 4.2V. It is measuring one nominal 4V cell, hence removed R7 making the resistor divider. In the video Dave used a 10K/10K divider as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V |
| StillTrying:
"as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V" I'd bet his V+ was 8.4V. |
| anishkgt:
--- Quote from: StillTrying on April 23, 2019, 09:18:57 pm ---"as he was measuring two cell in series, ie: 6v thru 8.4v, the divider was used to drop pin#5 to 3V thru 4.2V" I'd bet his V+ was 8.4V. --- End quote --- Yes he was that was why the 10k/10k voltage divider was used to drop it down for SIG(pin 5). Www.Georgehobby.wordpress.com Equipments: DSO104z, Hakko FX888D, Brymen BM869s Sent from my iPhone using Tapatalk |
| StillTrying:
"10k/10k voltage divider was used to drop it down for SIG(pin 5)." Some divider is need to keep SIG 1.4V below V+. I changed the resistors in LTs LM3915 to work as an LM3914, and using the the values I posted in Reply#5 it's not too bad with V+ 3 to 4.2V and SIG 1.5 to 2.1V. Bottom of the plot is the 10 LED currents, they're probably too high 4 or 5mA would do. Edity. If I was using this to monitor 18650 charging I'd make to top 3 LEDs 4.1V, 4.2V, 4.3V, I've seen 18650 get very warm very quick at 4.3V. |
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