Voltage Memory circuit - Page 1
Forum section: electronics / projects

author: FTVlog
author_rank: Newbie
timestamp: May 27, 2015, 01:29:57 pm
content: Hi,I'm looking of some kind of memory like "1 bit memory circuit" but instead of bits i want store voltages.For better understanding like the "1 bit memory circuit" if I send 1 bit it store and output 1 until reset, so, what i looking for is similar but with voltages, if i send 1 bit with one volt it store and output 1 volt until reset or new bit with voltage.I don't have any clue...Any ideas???

author: rolycat
author_rank: Super Contributor
timestamp: May 27, 2015, 01:34:15 pm
content: http://en.wikipedia.org/wiki/Sample_and_hold

author: FTVlog
author_rank: Newbie
timestamp: May 27, 2015, 03:54:38 pm
content: Hi rolycat,thanks for the fast reply.I'm trying to get an working circuit but i only find bad ones

author: FTVlog
author_rank: Newbie
timestamp: May 27, 2015, 04:46:31 pm
content: hi,I already look for sample and hold circuits but i don't find one working diagrammy idea is very similar with the tft pixelbut instead of Liquid crystals i need handle a LEDAny Idea?

author: paulie
author_rank: Frequent Contributor
timestamp: May 27, 2015, 04:56:24 pm
content: ...

author: dom0
author_rank: Super Contributor
timestamp: May 27, 2015, 04:57:32 pm
content: If this is about controlling large matrices of LEDs: don't even try to do it with thousands of S/H+ driver stages and long multiplexing lines. Use either digital multiplexing and PWM/PDM to control intensity or smart LEDs with a built-in digital bus (i.e. WS2812).By the way, there where real "voltage memories" once: bucket-brigade devices. They're essentially a chain of S/H stages.

author: FTVlog
author_rank: Newbie
timestamp: May 27, 2015, 06:29:09 pm
content: Hi paulie,I think it work for me thanks

author: FTVlog
author_rank: Newbie
timestamp: May 27, 2015, 06:38:59 pm
content: Quote from: dom0 on May 27, 2015, 04:57:32 pmHi dom0,I don't get your point,i just want a simple way to control an led light without stay always controlling in real time, but release the IC to do other stuff.the idea is very similar with the TFT matrix just that,I'm no inside of large Led matrix however on first view use this circuit to handled a led matrix maybe work.using digital components means using a lot of stream of data when the matrix be larger and larger and far away to be user friendlyCan you explain better you point?Thanks for reply

author: dom0
author_rank: Super Contributor
timestamp: May 27, 2015, 07:13:26 pm
content: For controlling many LEDs this approach requires one S/H per LED, which is a lot of components, compared to digital row+column multiplexing or smart LEDs, which don't need additional components for every single LED.If, however, you only want to control a single LED you can do that with a S/H. On the other hand I can't quite see how controlling a single LED poses any significant workload to any MCU.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: May 27, 2015, 11:32:46 pm
content: Quote from: FTVlog on May 27, 2015, 06:38:59 pmLike dom0 says, this is hardly a problem even for a Commodore 64. What "IC" are you talking about? It's hard to help when all we can do is guess.You absolutely want to control a LED with an analog voltage? Then why not just use a 6 pin I2C DAC, write to it, and there you go?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 28, 2015, 01:45:29 am
content: If we're talking period hardware, it may be relevant:I've taken apart some older computing hardware (printers, tape drives), which had a few large boards chock full of logic, and ultimately, a Z80 processor or two. The motor driver, I believe, had a pair of analog outputs for driving the tape reel spindle motors; probably a bunch of inputs as well. On the main logic board, there was clearly an S&H design: an 8-bit DAC (R-2R ladder and switch chip), followed by op-amps and stuff, and a few analog muxes (CD4xxx something). The op-amps weren't JFET, as I recall, so presumably they would leak down and need periodic refresh, but even with a Z80, updates in the 10kS/s range would've been easy enough to do. (May've also been some SAR ADC action with a nearby comparator, I don't remember.)Tim

author: bson
author_rank: Unknown
timestamp: May 28, 2015, 02:08:06 am
content: This is all very strange since LEDs aren't voltage devices. They have very low resistance, a nearly fixed forward voltage drop, and light up according to the current they're fed.Are you trying to replace an indicator lamp with an LED? Or something else?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 28, 2015, 02:50:14 am
content: Presumably with a current-transforming resistor inbetween...

author: FTVlog
author_rank: Newbie
timestamp: May 29, 2015, 01:06:57 am
content: Hi every one,Lets suppose (I'm curious about this) I go make an LED matrix 10X10, i can handle like a TFT right?Mount the apparatus with arduino just for play a bit.Lets make the Digital VS Analog with this scenario....Im getting lost, because, maybe we get fast delay with a limited connection...

author: rolycat
author_rank: Super Contributor
timestamp: May 29, 2015, 09:40:19 am
content: If you are curious, for a 10x10 LED matrix you could reduce the number of S/H elements by using 10 in a column and multiplexing the rows. Analog Devices make a couple of (expensive) 8-channel S/H ICs, so you could make an 8x8 matrix with just one of these.However, if you just want to reduce the processing and the number of connections from your main microcontroller it would probably be simpler and cheaper to use a separate display controller.