Hi All,

I am trying to display the following shapes on one 7 segments display depending on three control signal .if one of them high i want to display the first shape if the second one high i want to display the second shape and so on ^^



can i do that without using any controller ?!

Thanks in Advanced

 

Hi All,

I am trying to display the following shapes on one 7 segments display depending on three control signal .if one of them high i want to display the first shape if the second one high i want to display the second shape and so on ^^

View attachment 138362

can i do that without using any controller ?!

Thanks in Advanced

Probably easier in the long run to use a OTP ROM, but they're getting hard to find. The capacity will be more than you need, so you could just go for the full ASCII CHR set. There used to be off the shelf ROM chips, but I haven't seen one for decades.

Some TV sets shifted the bit pattern for all the digits at once into a SIPO shift register.

 

All you need is a bunch of diodes and resistors. See this https://i.stack.imgur.com/XRe0Q.png, but I would use a separate resistor in series with each diode, instead of bunching them up together.

 

All you need is a bunch of diodes and resistors. See this https://i.stack.imgur.com/XRe0Q.png, but I would use a separate resistor in series with each diode, instead of bunching them up together.

thank you

and what the value of each resisor ?

Probably easier in the long run to use a OTP ROM, but they're getting hard to find. The capacity will be more than you need, so you could just go for the full ASCII CHR set. There used to be off the shelf ROM chips, but I haven't seen one for decades.

Some TV sets shifted the bit pattern for all the digits at once into a SIPO shift register.

thank you for your appreciated effort

 

and what the value of each resisor ?

Just the usual calculation for whatever led and supply voltage you are using.

 

All you need is a bunch of diodes and resistors. See this https://i.stack.imgur.com/XRe0Q.png, but I would use a separate resistor in series with each diode, instead of bunching them up together.

If you like doing things the hard way on a large PCB area. Its basically building you own hand wired ROM.

Very small OTP ROM chips were very common at one time. There's still some of availability of EPROM chips and a fair choice of EEPROMS.

The redundant capacity is a small price to pay to get out of hand wiring a board full of diodes.

 

Hi All,

I am trying to display the following shapes on one 7 segments display depending on three control signal .if one of them high i want to display the first shape if the second one high i want to display the second shape and so on ^^

View attachment 138362

can i do that without using any controller ?!

Thanks in Advanced

Just three patterns -- and THOSE three patterns?

What if more than one of your three control signals is HI? Or what if none of them are HI? Or is your system such that you are willing to assume that exactly one of your control signals is HI at all times?

 

If you like doing things the hard way on a large PCB area. Its basically building you own hand wired ROM.

Very small OTP ROM chips were very common at one time. There's still some of availability of EPROM chips and a fair choice of EEPROMS.

The redundant capacity is a small price to pay to get out of hand wiring a board full of diodes.

OP said he needed only those three symbols, so a few diode seemed simpler than learning how to program an eeprom.

 

I agree, agree 7 diodes and resistors is pretty easy.

 

The E and F segments are allways on so they just need connecting to the supply via resistors. For the "0" display you need four diodes feeding segments A, B, C, D from the control signal. For the "L" display you need one diode from the control signal to the D segment. For the "H" display you need three diodes feeding the B, C, G segments from the control signal. You will need a current limiting resistor on each segment. For someone to draw the schematic you need to specify if the display is common anode or common cathode, The supply voltage and the required segment current.

Les.

 

OP said he needed only those three symbols, so a few diode seemed simpler than learning how to program an eeprom.

Just those symbols are OK with diodes, but adding more later can get out of hand fast.

AFAIK: a flash EEPROM only needs a few logic gates to sequence the select pins in the right order. There's no weird & wonderful Vpp levels to deal with. 0.3" footprint EEPROMS were fairly common on PC motherboards not all that long ago. It might even turn out that the EEPROM chip turns out cheaper than the bag of diodes, and could easily take less board space.

 

Here is an outline, assuming Vdd = 5V, display = common cathode @ 5 mA.

 

Just those symbols are OK with diodes, but adding more later can get out of hand fast.

AFAIK: a flash EEPROM only needs a few logic gates to sequence the select pins in the right order. There's no weird & wonderful Vpp levels to deal with. 0.3" footprint EEPROMS were fairly common on PC motherboards not all that long ago. It might even turn out that the EEPROM chip turns out cheaper than the bag of diodes, and could easily take less board space.

I also thought about to use EEPROM and I did something like that before, but it was more and more complicated, if the TS no any acknowledge about that or no any EEPROM writer then that is the problem or the schedule will be delay.

 

Diode logic comes to mind If you need more help w/ this tread PM me?

BTW are the dispays common anode or common cathode?

 

I used common anode 7 seg LED. And if you want to prevent getting different LED patterns when pushing >1 switch, then you need to add priority encoder before the switches.

 

What happens when more than one condition is met?
That’s for the OP, not a question for @absf to explain.

Nice work, by the way @absf.

 

I used common anode 7 seg LED. And if you want to prevent getting different LED patterns when pushing >1 switch, then you need to add priority encoder before the switches.

View attachment 138387

Try to use three 74LS17 and give up the ULN2003, how about that?

 

At first, I tried with 4049 inverting buffers but I was surprised that the voltage at the o/p of the buffers was >2V and I have to reduce the current limiting resistors to 100Ω. So I immediately think of using ULN2003 (max 500mA), though a TTL LS should work too sinking about the same amount of current.

Allen

[edit] I checked with 74LS17 datasheet. It has the advantage of the schmmitt trigger inputs and can prevent contact debounce. But its I(OL) is only 8 mA (per gate?), so not sure if it can drive 6 segments in "0"

 

At first, I tried with 4049 inverting buffers but I was surprised that the voltage at the o/p of the buffers was >2V and I have to reduce the current limiting resistors to 100Ω. So I immediately think of using ULN2003 (max 500mA), though a TTL LS should work too sinking about the same amount of current.

Allen

When you using the cmos and still want to get the higher current then you can choose as the inverter 74HC4049 or the buffer 74HC4050.

 

[edit] I checked with 74LS17 datasheet. It has the advantage of the schmmitt trigger inputs and can prevent contact debounce. But its I(OL) is only 8 mA (per gate?), so not sure if it can drive 6 segments in "0"

SN74LS17 from TI and it provides the max current is 40 mA, please check the bottom of the page 2, digikey still has the SN74LS07DR sale online, so this kind of product still has its market.