DIY: 5 position detector using 7400 series logic ICs - Page 1
Forum section: electronics / projects

author: TiTanerCZE
author_rank: Contributor
timestamp: May 26, 2016, 01:31:59 pm
content: Hi ,I made simple device using discrete 7400 series logic ICs , it's a 5 position detector for fun.Video(low resolution):Schema is attached.

author: Yansi
author_rank: Super Contributor
timestamp: May 26, 2016, 01:45:03 pm
content: And the purpose of such thing with bloated barely readable schematic is.... ??Purpose of IC6B/C/D, IC4E/F, IC5E/F (their output resistors respectively), R6, R8, R10, R12, R15 ...?? Why those T1 to T5 even there? Wtf?There was recently a thread about drawing readable and easily understandable schematics. You might want to look that up. Having a bunch of gates or flip flops and a fuckton of net names really isn't going to cut a mustard.

author: TiTanerCZE
author_rank: Contributor
timestamp: May 26, 2016, 02:00:07 pm
content: 1. For fun.2. Purpose of IC6B/C/D, IC4E/F, IC5E/F, none, so i put them to ground using a resistor.3. Current 30 mA for my ICs is not the best.4. I want to look that up.

author: Yansi
author_rank: Super Contributor
timestamp: May 26, 2016, 02:42:44 pm
content: Why would one load unused CMOS gate outputs with 10k resistor? That is for fun too?No reason for that whatsoever.30mA? Certainly no. Where are those 30mA flowing? Through the LED? I don't see any 30mA LED current in the schematic. A decent LED will be bright enough at 5mA and an average CMOS chip from the HC family will sufficiently drive up some tens miliamps (usually 35mA maximum?) from its output. (But keep in mind, that the overall supply pin current has to be 70mA maximum. So even if the chip has 6 outputs capable of 35mA each, you have to limit the load so that the supply pin current is no more than 70mA). Refer to each device datasheet for details.Conclusion: No need for transistors for small LEDs.

author: TiTanerCZE
author_rank: Contributor
timestamp: May 26, 2016, 03:36:41 pm
content: Ok, thank you, i made few changes, here there are:

author: Yansi
author_rank: Super Contributor
timestamp: May 26, 2016, 03:47:35 pm
content: Well done then. Now the schematic is readable and understandable in an instant.(Now I can also understand what it does, easily).Btw, where did those unused gates go? Unused CMOS gates should still have a well defined states on all of their inputs. Outputs can be left open with no issues.Also a good practice should be to disperse some more decoupling caps into the circuit, but I know, no fancy highspeed stuff, so it works fine now. Beware, one don't have to use high speed clocks or so in the system, the fast logic gates can get unstable on their own, when the supply design is too bad. The flipping of the gates may introduce some ringing in the supply nets, and that may cause instability in the whole circuit. (More prone to these issues if you are on breadboard using long wires and no supply decoupling caps).

author: Zero999
author_rank: Super Contributor
timestamp: May 26, 2016, 07:56:07 pm
content: Save an IC. Use an OR gate (74HC02/74HC32) for CLK1 and CLK2.Just to be picky about the drawing: get rid of the wite space and use PNG, rather than JPG format.