BK Precision 2709B beeper modification -- on/off switch with LED indicator - Page 1
Forum section: electronics / projects

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 22, 2014, 09:06:38 pm
content: The 2709B has a beeper that is a problem in quiet environments and there's no way to turn it off. What I'm going to try to do is put a switch in but I also want to use a translucent switch button so that when the beeper is disabled, instead of an audible beep, an LED flashes through the button membrane. I guess I don't care if the LED flashes along with the audible beep if that will make it simpler/easier.Things I'll need to know:Voltage required to beep, will it be enough to light an LED?How much pressure to press the switch, what's the metric mean in laymen's terms? 120gf??If it's flush mount or stand out?My questions are:1) Does anyone know of an off-the-shelf switch like this?2) How to implement if there's no off-the-shelf part?3) Opinions on location/placement of button4) What have I missed?

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 25, 2014, 04:51:34 pm
content: I still know very little about switches, digikey has 1000s of them. I at least know the correct term for what I need.SPDT - Single-pole double-throw. This should be a good very basic project for me. The hardest part may be finding the right switch. Digikey has switch kits but they're expensive and I wonder if they're worth it???I think I may need to devise my own switch for this application.I was going to try creating a schematic in kicad but had issues with kicad. My next attempt will be to try fritzing as it seems to be simpler and lightweight. A schematic for this is just a simple way for me to learn a thing or two.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 25, 2014, 08:39:23 pm
content: Here's my first ever schematic. I haven't measured any voltages for the beeper since my 2nd multimeter is sick so I don't know if the LED will require any other parts.

author: m12lrpv
author_rank: Regular Contributor
timestamp: March 26, 2014, 03:39:45 am
content: You'll want a current limiting resistor. If voltage is an issue look for one with a low dropout voltage. i.e. Red may be better than Blue.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 26, 2014, 11:33:05 pm
content: Quote from: m12lrpv on March 26, 2014, 03:39:45 amOk maybe orange, red ok too. I just gave myself an LED lesson. I'm still trying to work out the button. There are some expensive buttons at digikey. I may buy a cheap one and alter it by adding the LED.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: April 14, 2014, 04:00:24 am
content: I've gone down the switch rabbit-hole. I naively thought I'd just go on over to digikey and type in "switch led spdt" and voila! out comes a small list of potential switch candidates. The laugh's are one me! Some of the switches are quite expensive but they're nice of course.In my local search I found some push button momentary switches that were practically free and didn't work.(were clogged with some kind of dust)I found some spst switches that are through-hole have no part # but have a nice clicky feel to them. Close to free.But still don't have the right switch yet.Half my time was spent sorting out the switch jargon. SPDT, SPST, DPDT, DPST, momentary. Surface mount, panel mount, vandal-proof, tamper proof. But a good learning experience. Definitely the best way to learn is to embark on a project, any project.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: April 15, 2014, 04:04:17 pm
content: pickle9000 suggested this in another thread (https://www.eevblog.com/forum/testgear/lower-continuity-volume-beeper-on-fluke-87-v/)"It would be nice to have a 2 part switch. A reed for inside and a magnet on a slider (sticky back) for the outside. No holes or destruction."I have lamented about putting a hole in the meter case but I want a led to flash instead of the buzzer to beep (or buzz).That's why I decided on the SPDT switch. The meter will have two modes, beep-mode or led-flash mode.If I do it right and find the right switch and mount it correctly I might be able to maintain the case's integrity and even make it look as if it's factory.

author: pickle9000
author_rank: Super Contributor
timestamp: April 15, 2014, 04:23:34 pm
content: Hows the access to the side of the lcd? Does it have a backlight? Making the display turn red could work.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: April 15, 2014, 05:35:12 pm
content: Quote from: pickle9000 on April 15, 2014, 04:23:34 pmIt has a backlight. Not sure about access to the side of the lcd. I understand you're saying to add a red led internally and drive the led output into the side of the lcd. That's a good idea, I will look at that. It retains the low power of an led, removes the need to put a hole in the case and would allow removal later if wanted with none the wiser.I'll have to fix my micronta first so I have a backup meter.

author: mikro
author_rank: Contributor
timestamp: February 01, 2015, 06:07:44 pm
content: Have you completed your mod on the 2709b multimeter? I have the same model, and the buzzer, when changing modes has been annoyed me since i got it. Has anyone found a different method silencing the buzzer (only when changing modes), like modifying the circuit? or is the buzzer controlled from the IC with the same signal that is used on continuity tester beep.

author: david77
author_rank: Frequent Contributor
timestamp: February 01, 2015, 06:56:42 pm
content: The beeper of my 2709 has always annoyed me, too. So I simply added a resistor in series with the buzzer. Don't remeber the value now, maybe 1k?You can easily find the right value by experimenting.Now the beep is still there but it's not annoying anymore when working at night and no ugly holes drilled in the meter. I really would not do that.

author: mikro
author_rank: Contributor
timestamp: February 03, 2015, 09:45:58 am
content: I just wouldn't want to make the continuity buzzer more silent. From the datasheet i figured that the buzzer, when changing modes, is hard coded, so no magic pins to pull down to disable it. Instead I found that in the frequency mode, when you pull down pin 80 'VAHZ', you get into the duty cycle mode. I briefly tested it from the calibration output from my scope, and in showed it right (50%). Weird that they didn't implement this mode to the DMM.