Path: news.uiowa.edu!uunet!in2.uu.net!newsfeed.internetmci.com!206.229.87.25!news-peer.sprintlink.net!news-backup-west.sprintlink.net!news-in-west.sprintlink.net!news.sprintlink.net!Sprint!151.164.30.38!newsgate.swbell.net!swbell!not-for-mail From: Rubywand Newsgroups: comp.sys.apple2 Subject: Re: Bi-color red/green LEDs: Disk II read/write???? Date: Sat, 14 Mar 1998 18:36:36 -0600 Organization: Southwestern Bell Internet Services, Richardson, TX Lines: 84 Message-ID: <350B2294.929D0294@swbell.net> References: <6eeq9s$mhc$1@lynx.unm.edu> Reply-To: rubywand@swbell.net NNTP-Posting-Host: ppp-207-193-12-217.hstntx.swbell.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: (null) 889922047 4837 (None) 207.193.12.217 X-Complaints-To: usenet@nnrp3 X-Mailer: Mozilla 4.04 [en] (Win95; I) Xref: news.uiowa.edu comp.sys.apple2:133622 stephen e buggie writes ... > > A store is clearing out bi-color LEDs red/green. These LEDs have three > wires: black (negative), red (red +), green (green +). > > I want to add the bi-color LED to my Disk II drives, so that it will glow > GREEN for READ, and RED for WRITE. I already have an AE 3.5" 800K drive > that does this, and it looks nice. This will be a third enhancement to > Disk II --- "Super Bugg-Drive." > > First, what value of resistor should be added? The ad says these are 2 > volt LEDs, and that 20 milliamps should flow through the LED. > > Will the 20 milliamps affect the read/write performance of the drive in > any way? > Since you would be sticking a 20ma load onto a 74LSxxx TTL output in each case, the odds are pretty good that Read and Write data would be screwed up. One idea is to use a couple general purpose PNP transistors. The LED GND lead goes to GND. The Red lead goes through a 150 or so Ohm resistor to the Collector of the "Write Transistor". The Green lead goes through a 150 or so Ohm resistor to the Collector of the "Read Transistor". Each transistor's Emitter goes to +5V. The Base of each transistor has a 1k or so Ohm resistor attached. The resistor connected to each Base is the Input for that LED. This should take care of driving the LEDs. When an Input goes Low (e.g. to GND), the corresponding LED should light. If you feel brightness is too high, increase the Base R value. The rest of the circuit depends upon the conditions you choose for lighting an LED and how many of what kinds of IC's you have in your parts bin. For example, you could use the condition: when /Enable is low and /WR-REQ is low then /WR-LED is low. /WR-LED goes to the Write LED (Red) Input. If /Enable is low and /WR-REQ is high then you assume a Read and /RD-LED goes low to turn on the Read (Green) LED. A single quad dual input NOR IC, like a 74LS02, could handle the logic. In the circuit below, "[ ]" numbers are Disk ][ Analog board connector points and "( )" numbers refer to pins on a 74LS02. [10] /WR-REQ ------ (2) NOR-1 (1)---- (5 & 6) NOR-2 (4)---- /WR-LED to Red Input [14] /Enable -------(3) | _________________________| | | |__________(11) NOR-3 (13)--- (8 & 9) NOR-4 (10)--- /RD-LED to Green Input [14] /Enable -------(12) (7) to GND (14) to +5V In the above, when /Enable is low, one of the LED's will light. If /WR-REQ is low, the Red LED will light; if /WR-REQ is high, the Green LED will light. (Some fiddling with resistor values may be required to settle on the right ON brightness levels.) One advantage of this circuit is that you always have a 'drive ON' indicator and, so, do not need to drill a hole for another LED. An alternative circuit could monitor actual Read [16] and Write [18] activity using /Enable [14] to enable inputs to a dual 1-Shot IC. Write transitions would fire the Write 1-Shot; Read transitions would fire the Read 1-Shot. The /Q output from a 1-shot would connect to the desired Red or Green Input. Pulse time for each 1-Shot could be something like 1/5 second in order to guarantee a stable, bright display. Rubywand