Hmmm. The hourly chime function didn't function last night when I assembled said clock. Didn't chime at 7 am this morning. It did chime (3 harsh beeps, one second apart) at 8 am and continues to do so. Apparently it thoughtfully self-silences in the evening hours, much like a stately grandfather clock. Nice touch!
I got one of my 4-bit clock kits but it doesn't seem to exactly match these instructions. Actually, it's pretty obvious where all of the parts go except the polarity of the electrolytic capacitors. My kit has two. The legend on the PCB has a circle where one half is colored in black. I thought maybe this meant that the black side was plus since the cap has a white band on the minus side. However, the legend for one of the two caps is also marked with a "+" on the white side of the circle. Any idea which way they should be inserted?
Normally the white block on the overlay would mark the negative. But you cannot guarantee that with so many pcbs being designed by amateurs these days, you cannot be certain that standards are being followed
Best to check it with a meter like jmg recommended.
+1 to doing some trace-sleuthing with an ohmmeter. Much like "measure twice, cut once". A reversed electrolytic cap likely won't blow up but damage can be done. They do blow at surprisingly low voltage. This reversed 16V cap blew at 25V.
BTW it's nice to hear you fellows are also building these silly little kits I post about. I find them to be quick, satisfying builds and I actually love soldering, lead and all.
If the 10uF cap you have, meant to be assembled at the lower left corner of your board, has a solid connection to 5V and is in series with a 4k7 Ohm resistor. that, in its turn, is connected to GND, then it should be part of the reset circuit (89C2051, pin1), as depicted at the upper left corner of the linked schematic.
As for the 100uF cap, at the middle right of the board, it seems to be connected as a decoupling cap, being part of the 5V input pins filtering circuit.
Both silkscreened symbols seems to agree, as to be interpreted as the hashed side being the (-) pin orientation.
Althought you've not posted the copper side, the board traces at those sites could confirm my guess, at a glance.
BTW it's nice to hear you fellows are also building these silly little kits I post about. I find them to be quick, satisfying builds and I actually love soldering, lead and all.
Thank you! It has been interesting comparing and contrasting your board and David's. It has also been interesting investigating the 2051 chip. 35 years ago I didn't care for the 8051. A smaller footprint, CMOS, and 6x MIPS have improved my opinion.
@David: Ironic that the board I received looks just like the one you thought you were getting.
FWIW, it went together quickly and worked as advertised.
Which is better? The erco board is cuter and the software more developed. But the DB board is sharp-looking, roomy, and likely an excellent educational tool for an interested niece or nephew. The educational value may not stop there...The 2051 begs to be reprogrammed and have greater functionality added.
If the 10uF cap you have, meant to be assembled at the lower left corner of your board, has a solid connection to 5V and is in series with a 4k7 Ohm resistor. that, in its turn, is connected to GND, then it should be part of the reset circuit (89C2051, pin1), as depicted at the upper left corner of the linked schematic.
As for the 100uF cap, at the middle right of the board, it seems to be connected as a decoupling cap, being part of the 5V input pins filtering circuit.
Both silkscreened symbols seems to agree, as to be interpreted as the hashed side being the (-) pin orientation.
Althought you've not posted the copper side, the board traces at those sites could confirm my guess, at a glance.
Which is better? The erco board is cuter and the software more developed. But the DB board is sharp-looking, roomy, and likely an excellent educational tool for an interested niece or nephew. The educational value may not stop there...The 2051 begs to be reprogrammed and have greater functionality added.
If you reprogram, the AT89C2051 needs 12V, or there are AT89LP2052, AT89LP4052 parts that are 5V SPI programmed.
Addit: I see a ZIF programmer on eBay SP200SE for sub $10
For new designs, these days you would use a newer 51 variant like N76E003/N76E616 for wide Vcc, or EFM8UB1/2/3 for USB. STC8F is also interesting.
Some cheapie eBay LEDs have the flat plastic on the wrong edge ...
Some not-so-cheap LEDs are that way, too; so I'm not so sure there's a "right" or "wrong" edge for the flat side. I always go by lead length, not the flat side, to determine an LED's polarity.
Well, I assembled my clock but it doesn't seem to work. I got a brief flash of something on the LED display and then nothing. I'm feeding 5v into the power terminals. Nothing smoked or got hot so I'm not sure what went wrong. I measure 4.3v on pin 20 of the AVR chip.
Does the flash at the displays repeats, each time you feed 5V to the board, having waited some time, allowing for the reset circuit to discharge the 10uF cap, during the interval?
Or it was a single event (display flashing), at first power on?
Does the flash at the displays repeats, each time you feed 5V to the board, having waited some time, allowing for the reset circuit to discharge the 10uF cap, during the interval?
Or it was a single event (display flashing), at first power on?
Also, at the schematic I've linked before, the reset pulse is timed by means of a 10K resistor, and your board uses a 4k7 one.
Then, your board current reset pulse would last, roughly, 50% shorter than it would be, if the resistor value is doubled.
Perhaps it worth trying, If you have a 10k part available, into some spares shelf.
Also, checking the datasheet, it reveals that the AT89c2051 has indeed an internal pulldown resistor at pin 1 (nom. 100K Ohm), connecting it to GND, and, at the same time, the minimum input voltage, during reset, should be 0.7 x Vcc (~3.5V), so that's the reason for the huge 10uF cap (lower ESR than a smaller one) and the auxiliary 4k7 (could be 10k) bleeding.
At the datasheet, RST must be active (higher than 3.5V) for two clock cycles, at least, to be recognized. The current setup does surely has ample provisions for it.
Given the cap value, perhaps even a digital VOM could be used to check you don't have an open 10uF cap, messing with your expectations.
But, at the same time, if the crystal oscillator isn't turning on, at all, then it can be the culprit for the whole clock to don't work as expected.
Some circuits use to call for a 1-10MOhm resistor, paralleled to the crystal pins, to make it start sanely. Others don't.
Since I dont have any experience with that Cpu at all, I'm limited to the very basics, ATM.
P.S. You have answered to my last post, while I was typing and translating this one.
Provided you could use some instrument to verify the RST pin waveform, and if it could be eliminated as the obvious culprit, it rests to try checking the crystal, thought it would be not so easy to verify, because you will need an oscilloscope to do this check.
Withou a scope, perhaps the MOhm-ranged resistor could do the trick for you, since it could be easely soldered at the crystal pins.
Here is another piece of information that I didn't mention before but since you say the crystal could be an issue I'll mention it now. I initially soldered the crystal into the position that was supposed to contain C5 so I had to unsolder it and move it to the correct position. This seems to have gone okay but could I have damaged the crystal in the process?
C5, the 100nF decoupling cap? It is directly connected between the 5V and GND lanes. Oh, oh! I'm not sure, since I've didn't done this before, but you surely could account for this as a true clue of what has gone. (Gone xtal; it could be an enlightening expression here).
Have you another equivalent xtal at hand? It don't need to be at the same frequency. Even a 6MHz one, of the same cut type will work, despite the anoying flicker at the scanning display.
C5, the 100nF decoupling cap? It is directly connected between the 5V and GND lanes. Oh, oh! I'm not sure, since I've didn't done this before, but you surely could account for this as a true clue of what has gone. (Gone xtal; it could be an enlightening expression here).
Have you another equivalent xtal at hand? It don't need to be at the same frequency. Even a 6MHz one, of the same cut type will work, despite the anoying flicker at the scanning display.
I didn't power it up with the crystal in the wrong place. BTW, I tried a 10K resistor in the reset circuit and that didn't help. I do have a scope so maybe I'll try hooking that up to see if the crystal is working at all.
Sorry, my bad! I've wrongly assumed you did powered it, with the crystal at the wrong place.
If you can verify it, with the help of the scope, it'll be super.
In case it's dead, and the MOhm resistor trick doesn't help, and you don't have another one, but does have a ceramic ressonator at hand, you could try it, but the 30pF caps should be changed too, using two 40pF ceramic ones, in the same place.
P.S. If one of the 30pF caps is internaly (or externaly) shorted, then this is a no-go situation, but the scope (then, a meter to confirm the shorted item) could help you find it.
No problem at all! It is this shape, since it is a crystal, not a digital oscillator, wich would have a squared waveform.
Have you checked the sip resistor pack pin 1 position? It should be marked at the pack, as a dot or straight bar, near pin 1. And it should be soldered towards the 5V suply, Cpu pin20.
No problem at all! It is this shape, since it is a crystal, not a digital oscillator, wich would have a squared waveform.
Have you checked the sip resistor pack pin 1 position? It should be marked at the pack, as a dot or straight bar, near pin 1. And it should be soldered towards the 5V suply, Cpu pin20.
I was careful when I soldered in the resistor pack not to get it backwards as it would be nearly impossible to unsolder. The dot on the resistor pack is near pin 20 of the CPU.
Comments
The 89C2051 has Vdd on pin 20, GND on Pin 10 and both caps should be +ve to Vdd, so an ohmeter, or PCB trace follow should sort polarity.
Best to check it with a meter like jmg recommended.
BTW it's nice to hear you fellows are also building these silly little kits I post about. I find them to be quick, satisfying builds and I actually love soldering, lead and all.
Back in the day my friend built a circuit with a 10,000uF, 500 volt electrolytic in the power supply. A huge 1 liter can of a capacitor.
When that thing blew the whole lab was full of "snow". No doubt toxic.
The schematic that seems to closely match your board, is available at:
theradioboard.com/rb/viewtopic.php?t=6279
If the 10uF cap you have, meant to be assembled at the lower left corner of your board, has a solid connection to 5V and is in series with a 4k7 Ohm resistor. that, in its turn, is connected to GND, then it should be part of the reset circuit (89C2051, pin1), as depicted at the upper left corner of the linked schematic.
As for the 100uF cap, at the middle right of the board, it seems to be connected as a decoupling cap, being part of the 5V input pins filtering circuit.
Both silkscreened symbols seems to agree, as to be interpreted as the hashed side being the (-) pin orientation.
Althought you've not posted the copper side, the board traces at those sites could confirm my guess, at a glance.
Hope it can help a bit
Henrique
Thank you! It has been interesting comparing and contrasting your board and David's. It has also been interesting investigating the 2051 chip. 35 years ago I didn't care for the 8051. A smaller footprint, CMOS, and 6x MIPS have improved my opinion.
@David: Ironic that the board I received looks just like the one you thought you were getting.
FWIW, it went together quickly and worked as advertised.
Which is better? The erco board is cuter and the software more developed. But the DB board is sharp-looking, roomy, and likely an excellent educational tool for an interested niece or nephew. The educational value may not stop there...The 2051 begs to be reprogrammed and have greater functionality added.
If you reprogram, the AT89C2051 needs 12V, or there are AT89LP2052, AT89LP4052 parts that are 5V SPI programmed.
Addit: I see a ZIF programmer on eBay SP200SE for sub $10
For new designs, these days you would use a newer 51 variant like N76E003/N76E616 for wide Vcc, or EFM8UB1/2/3 for USB. STC8F is also interesting.
The hashed lines inside the caps silkscreened symbols, does in fact represents the position of their (-) pins.
Good soldering session!
-Phil
Pretty sure I've seen that (lead length) reversed too, in the nameless bins of LEDs I've hoarded away.
Or it was a single event (display flashing), at first power on?
Then, your board current reset pulse would last, roughly, 50% shorter than it would be, if the resistor value is doubled.
Perhaps it worth trying, If you have a 10k part available, into some spares shelf.
Also, checking the datasheet, it reveals that the AT89c2051 has indeed an internal pulldown resistor at pin 1 (nom. 100K Ohm), connecting it to GND, and, at the same time, the minimum input voltage, during reset, should be 0.7 x Vcc (~3.5V), so that's the reason for the huge 10uF cap (lower ESR than a smaller one) and the auxiliary 4k7 (could be 10k) bleeding.
At the datasheet, RST must be active (higher than 3.5V) for two clock cycles, at least, to be recognized. The current setup does surely has ample provisions for it.
Given the cap value, perhaps even a digital VOM could be used to check you don't have an open 10uF cap, messing with your expectations.
But, at the same time, if the crystal oscillator isn't turning on, at all, then it can be the culprit for the whole clock to don't work as expected.
Some circuits use to call for a 1-10MOhm resistor, paralleled to the crystal pins, to make it start sanely. Others don't.
Since I dont have any experience with that Cpu at all, I'm limited to the very basics, ATM.
P.S. You have answered to my last post, while I was typing and translating this one.
Provided you could use some instrument to verify the RST pin waveform, and if it could be eliminated as the obvious culprit, it rests to try checking the crystal, thought it would be not so easy to verify, because you will need an oscilloscope to do this check.
Withou a scope, perhaps the MOhm-ranged resistor could do the trick for you, since it could be easely soldered at the crystal pins.
Not many other options, ATM.
It worth verifying it, against the schematic, with a meter.
Have you another equivalent xtal at hand? It don't need to be at the same frequency. Even a 6MHz one, of the same cut type will work, despite the anoying flicker at the scanning display.
If you can verify it, with the help of the scope, it'll be super.
In case it's dead, and the MOhm resistor trick doesn't help, and you don't have another one, but does have a ceramic ressonator at hand, you could try it, but the 30pF caps should be changed too, using two 40pF ceramic ones, in the same place.
P.S. If one of the 30pF caps is internaly (or externaly) shorted, then this is a no-go situation, but the scope (then, a meter to confirm the shorted item) could help you find it.
Have you checked the sip resistor pack pin 1 position? It should be marked at the pack, as a dot or straight bar, near pin 1. And it should be soldered towards the 5V suply, Cpu pin20.
I'm trying to determine it it could have their leads bent out of order, comparing the tracks at the copper layer, with the silkscreen symbol.