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Tandgnissle

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Asayuki’s Logic Comparator Clone v 0.1
in7WkVg.jpg

Since Asayuki seems to have exited the hobby several years ago and the demand was there (including mine) I decided to clone his logic comparator with the help of the documentation they left at Arcade Otaku and Mike from leaded solder. While at it I found some errors in his documentation regarding the manufacture of the clip cable, a new use and if not an improvement then at least a change and cost cutting measure.

The new use case is to use it as a logic clip. Simply have all jumpers open and bind everything but pin 2 (VCC) together and the XOR logic chips will ensure that the leds light up upon a high state on the chip the clip is connected to. Keep in mind that floating pins will be seen as high by the 74LS86.

The change is adding more test points for GND and VCC which can be used in different ways. The most important thing is adding a test hook clip to a GND test point in order to connect that to a test point corresponding to the ground pin of the chip you're testing. This enables you to get away with using longer test clips than the chip you’re testing thus saving upwards of 50€/$ per clip cable you don’t need to build unless you can find them cheaply elsewhere. Additional test hook clips can be soldered on for both GND and VCC for connecting closer to the power source of whatever component you’re testing. If you have access to a 3D printer you can make some clips yourself, highly recommended if you have access to one and want to save quite a bit of money. Here is the link to the thingaverse files.

Lastly here are the new pinouts for the clip cables.
id5nmM3.png


Since the bill of materials are a bit old, here is a 2022 BoM:
digikey:
5 * 74LS86 296-14901-1-ND
19 * Green LED 754-1127-1-ND
1 * Horizontal IDC 20 Connector 1175-1618-ND
2 * 2x10pin stripes (needs to be cut down) S2012EC-10-ND
19 * resistors A129541CT-ND
1-4 * IDC 20 connectors LKR20H-ND
1-4 * Ribbon cables 3M157823-1-ND
20 * Jumpers 1849-09200-71-BDGB00-ND
7 * Capacitors 478-10054-1-ND
2 * 2x1 pin stripes (if careful you can use the ones from the 2x10 ones)
1 * 20 pin clip 923704-ND
1 * 18 pin clip 923703-ND
1 * 16 pin clip 923700-ND
1 * 14 pin clip 923698-ND
1 * 20pin ZIF 3M2002-ND
60 * Scope Test Point 4952K-ND

Zif's can be ordered from China a bit cheaper.

I do have some extra PCBs, kits and built ones I can sell, they'll be batch built and the gerbers will be released in sixth months or so.
Here is the sales thread.

When building the kit just follow what you see in the pictures. The only things with polarity is the LEDs and the arrow on their underside or the two dots on the top should point towards the edge of the board.

edit: Gerbers have been attached to the file.
 

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ekorz

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Got mine in today, thanks! I am surely doing something wrong, between the original documentation and what you wrote above. I’m just trying to test a known working chip in-circuit against another brand new known working chip.

SN74HC04N

AFE501C6-A53D-4C28-8121-F5D5545886B4.png


Vcc - leave open? (Jp20)
The orange test clip that’s soldered into tp50 - ignore?

Otherwise jumpers are
Left side starting at the top (jp1)
c o c o c o c(gnd)

Right side starting at the top (jp19)
c o c o c o with jp20 open for vcc

I only ask because I see a lot of LEDs firing and I thought that indicates failure.

1DFCF029-1432-4323-9EBA-5AC891E3B960.jpeg
 

Tandgnissle

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Hmm, that is weird. Jumpers are set correctly. LEDs lighting up slightly is no problem but it seems like four of the LEDs have almost full intensity. I'll need to see if I have a 04 myself and get back to you on that.
 

ekorz

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The LED intensity is just my camera and the lighting involved, they’re certainly visible but i turned down the ambient light in the room to capture the LEDs more easily. I tried other chips as well, they also show lit LEDs basically on any open jumper line it seems. I’m just wondering what expected behavior is for a good chip, and if I did anything wrong!
 

Tandgnissle

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Oh yeah I forgot to ask. Is the chip in circuit a HC too? If it's LS and you're comparing HC with LS you might have some problems.
74HC are CMOS Logic. 3.3V Vcc, way different thresholds for logic. Much smaller current.
I don't have any 04 to test right now, I should get some.
You might want to test some other logic chip.
 
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Tandgnissle

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Just tested 08 and 157
Code:
7408 14pin chip
1 C        X20 VCC X
2 C        19 C
3 O        18 C
4 C        17 O
5 C        16 C
6 O        15 C
7 GND C    14 O
8 O        13 O
9 O        12 O
X10X    11 O


74157 16pin chip
1 C        X20 VCC X
2 C        19 C
3 C        18 C
4 O        17 C
5 C        16 O
6 C        15 C
7 O        14 C
8 GND C    13 O
9 O        12 O
X10X    11 O


Those didn't light up at all.
158IHL3.jpg


Did a 74LS283 and that one lights up but not at full intensity. 283 is a 4-Bit binary adder so I'm not sure how well that works.
fIGoPsa.jpg

You see different intensities in the light there on some of the outputs.
 

_rm_

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"CONS – Jumpers are needed to configure the tool: they need to be fiddled with any time the reference IC is changed. A cheat sheet can be prepared to quickly search for the needed configuration based on the IC model, but that's just as much as one can do"

Don't want to create off-topic content, but does anyone know if such sheet already exist?
 

Tandgnissle

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Not that I know (and well it does belong here) . I can post the ones I've used but it's probably better if I start a wiki page or something on the arcadeotaku wiki.
 

_rm_

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Got the package today, haven't tried it yet but looks great.
Already printed the other clips in an epoxy 3d printer. Although the picture is far from great, the resolution on these looks amazing :

O2jxQaL.jpg
 

Tandgnissle

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Right so I've made a big mistake on the cables 18 pins and below.
Basically the reference IC has no ground which gives faulty readings.
What you can do as an interim solution is use the ground probe on the ground leg test point of the reference IC.
A permanent solution is splicing the lead on the cable.
1653161988618.png

The wire that is soldered there should still be there though.

Now since I feel quite bad about this I got two primary choices for people that bought this off of me.
1: €7 refund on all affected sub 20pin cables.
2: Send them back to me and I'll redo them properly (I'll pay for cheapest trackable freight both ways.)
I'll be sending this to everyone that bought these cables off of me and if it isn't enough we'll come to some sort of solution.
 
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xga

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Hi Guys. Received my Logic Comparator in the mail today (thanks @Tandgnissle) and wanted to test it out. I've got a board that has a bad LS245, so I thought it would be good to test it on a known working one and the one that has failed.

Looking at the logic gates for the LS245, it seems to me that only pins 1 and 19 are input (closed) and the rest are bi-directional (open) excluding gnd (pin 10) and Vcc (pin 20).

74LS245.png


So I then inserted a known working LS245 IC into the zif socket, placed jumpers on JP1 and JP19, connected the 20 pin probe to the logic comparator, then clipped onto a known working LS245 on the game PCB, and then turned the game board on. All the LED's (except pin 1 and pin 19 -both closed) lit up as seen in the photo below. My understanding is that the LED's should only light up when there is a difference or a fault. Is that correct?

IMG_0369.jpg


I then tested it on the known faulty LS245 IC and only some of the LED's lit up (I didn't take a photo).

Hopefully I am doing something incredibly stupid. The red ground clip doesn't need to be connected, does it? Perhaps the LS245 can't be properly tested with a logic comparator??
 
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Nebula

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Unfortunatelly, logic comparator doesn't work with ICs with bidirectional pins (i.e. pins that are changing between acting as input or output over time). That's why you are getting inconsistent results, because the instant when some pin is acting as an input (and thus produces an output at the other side of the ic), the logic comparator is not taking it into consideration, so the comparation is not valid in that instant.
 

xga

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Thank you, Nebula. That's very handy to know and makes sense.
 

_rm_

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Right so I've made a big mistake on the cables 18 pins and below.
Basically the reference IC has no ground which gives faulty readings.
What you can do as an interim solution is use the ground probe on the ground leg test point of the reference IC.
A permanent solution is splicing the lead on the cable.
1653161988618.png

The wire that is soldered there should still be there though.

Now since I feel quite bad about this I got two primary choices for people that bought this off of me.
1: €7 refund on all affected sub 20pin cables.
2: Send them back to me and I'll redo them properly (I'll pay for cheapest trackable freight both ways.)
I'll be sending this to everyone that bought these cables off of me and if it isn't enough we'll come to some sort of solution.
Just to make sure:

Is the current table on the first post correct?

Thanks
 
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