eBay Chinese Electronic Clock Kit

[Harvey]

Re: eBay Chinese Electronic Clock Kit

...
How do I know which way round the switch goes?

Try removing it, its a push to reset switch, if its fitted wrong it could be holding the MCU in reset.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

i hoped to find a real schematic ..
as an afterthought it should be easy enough to add a reverse polarity diode and fuse .. or even a bridge rectifier like some Philips radios had .

[eccerr0r]

Re: eBay Chinese Electronic Clock Kit

<sarcasm>My WALL CLOCK runs at 12MHz! osofast...</sarcasm>

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

I assumed that too, but its to be connected through a diode to the vcc supply... unless the MCU has voltage sensing and goes into backup (no display) mode below a certain voltage.

I also notice there is a resistor bypassing this diode (I can't make out the numbers on the circuit diagram) that CHARGES the 3V battery when connected to a supply! So DON'T use a standard 3V coin cell in there or you'll have another exploding component!.



*EDIT * What goes on with R12 on your PCB? Trick of the light or has that only got one band?

Yes it only has one band, but it came in the same strip as the others, so I think it is just a printing error.

Tbh I hoped I could just solder it all and it'd work

[petehall347]

Re: eBay Chinese Electronic Clock Kit

did you try it again yet ?

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

Pete

Still waiting on a replacement cap.

[goontron]

Re: eBay Chinese Electronic Clock Kit

<sarcasm>My WALL CLOCK runs at 12MHz! osofast...</sarcasm>

LOL. Well, if you want to play that game, My wall clock runs at 1200Mhz.

[stj]

Re: eBay Chinese Electronic Clock Kit

damn it, mine only runs at about 80Mhz.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

mine runs at 32.768 khz

[goontron]

Re: eBay Chinese Electronic Clock Kit

Oh, and my watch runs at 360Hz. Can anyone guess the watch?

[Harvey]

Re: eBay Chinese Electronic Clock Kit

Pete

Still waiting on a replacement cap.

Try it with a 9V battery, it won't need that cap.

[redwire]

Re: eBay Chinese Electronic Clock Kit

It's got a weird power supply. A 78L05 5V regulator then diode-drops D5 so the MCU runs off 4.3V and D6 for the LED display and colons. So on battery power, no LED's lit due to the blocking diode D6, and D5 also should have saved OP's parts from reverse-polarity. I would say the 78L05, C1, C2 are toast. It also micro-charges the lithium coin cell through R1 10k to +4.3V

You could try power it from 3 AA cells at 4.5V or remove the MCU and ensure the 5V rail works OK. It will work without C1 if the DC supply has a filter cap.

I can't believe how cheap these kits are. HS130110 SH-E 879 version.
I really like the other kits with DS3231 RTC, they don't drift.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

78L05 Regulator Features:
5V Positive Voltage Regulator
Output Current upto 100mA
Maximum Input Voltage is 30V
Operating current(IQ) is 5mA
Internal Thermal Overload and Short circuit current limiting protection is available.
Available in TO-92,SO-8 and SOT-89 package

[petehall347]

Re: eBay Chinese Electronic Clock Kit

whatever do they mean by "available " ?

[redwire]

Re: eBay Chinese Electronic Clock Kit

The 78L05 voltage regulator is offered in at least three different packages: TO-92 (through-hole), SOIC-8, BGA. Same IC inside.
It is the low current 100mA version of the LM7805 high current 1,000mA part in TO-220 and D2PAK packages.

I know from experience they die if you give them reverse voltage, at the input or output actually, like connecting a battery backwards to the output. Foof.

OP should verify it puts out 5V; not shorted and giving near raw value of the AC adapter or else the MCU will pop.

[Rulycat]

So should I remove any components? Or just feed to the usual screw input with 3 x AAs?

[stj]

Re: eBay Chinese Electronic Clock Kit

if you use 3 AA's you need to link the input and output of the 78l05
you can do that by touching them with a screwdriver - for a quick test.

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

Sorry gents will do this just waiting on the 3xaa battery box to arrive.

[Rulycat]

Re: eBay Chinese Electronic Clock Kit

It's working! Didn't have to short the 7805.

You'll notice I replaced the cap there as well.

Does this mean the transistor isn't cooked?

Haven't installed the switch yet.

[petehall347]

Re: eBay Chinese Electronic Clock Kit

regulator might be shorted