lcd clock

[jimmy88]

i assembled the same circuit of dr.acula which is on this link http://drvernacula.topcities.com/lcd_clock_for_controlling_pumps_.htm
and i downloaded the same code but the lcd is just showing squares there's no change when i push the buttons so its not working with me
is this circuit should be done by 1 or 2 hc595 because the schematic is showing only one

 

[inglewoodpete]

If the LCD is just showing squares, you need to adjust the contrast control voltage. Your circuit should have a trimpot to adjust Vo on pin 3 of the display.

 

[jimmy88]

i added 10k variable resistor but still squares the resistor is just making the squares getting darker or lighter until they fade out

 

[moxhamj]

If the circuit is built exactly the same it will work. But just one mistake with an LCD display and nothing will display at all. I turned that circuit into a PCB and built three of them this afternoon and it works well. But PCBs make life a lot easier! Can you post some photos please.

 

[jimmy88]

i did the circuit on a breadboard so millions of wires are there
even if i post photos i dont think that the circuit will be clear to you so you can identify a mistake i did on the board
btw, i didnt add R4 , R5 and i didnt use TP4 TP3 becouse i think those is for the download circuit i downloaded the program by other circuit

whats TP1 ,TP2 and TP5 ??

i saw two bubbles on the scematic on hc595 pin10,pin13 is this a NOT gate, i didnt add any gates ?

also i added an elctro capacitor that has polarity with the same value of 470uf while in the scematic the capacitor is non polorized is this going to effect ??

 

[hippy]

Black squares on LCD : Is usually a sign that something isn't wired exactly right. Check the data lines are to the correct HC595 / LCD contacts and not crossed-over etc. If not using a HD44870-based LCD you may need to change the initialisation routines slightly.

TP1 etc : These are "Test Points", used to indicate where test probes should be connected during debugging and turnd into contact pads on a PCB.

BH595 "bubbles' : These indicate that the inputs are inverted / active low. No need to add any external gates.

 

[moxhamj]

Post a photo anyway. I bet you my breadboards are messier than yours! Real breadboards are like that. But on the other hand, if you can't follow the wire connections...

BTW that code is not optimised. Hippy has come up with all sorts of clever optimisations that make it run faster. But start with it as it is.

At the very least, can you feed in a binary number to the senddatatolatch routine and check the high/low status of the display pins 4,6,11,12,13,14. Feed in %00000001, then do %00000010 etc and do it 8 times.

Addit - I just wired up another display tonight. And managed to have it not working on the first go. I forgot to ground pins 5,7,8,9,10. Everything has to be just perfect with these displays. Sometimes you have to start your program, put an End after the very first output of some data, then go through with a logic probe and measure each of the pins 1-14 and check they are exactly what they should be. Then run the program again with an End after the second output and test it again.