LMC555: Hi Kato or anyone who can help . Question is related to the CMOS LMC 556 1.5 V supply - From Andrew , North Wales - UK

Hi Andrew, 

The LMC555 is the CMOS version and the LM555 is the bipolar version. They both come in PDIP packages, which are spaced for a breadboard, as well as surface mount if you choose to switch when you finalize your PCB. As far as the dual package, there is no CMOS version of the LM556 (I do not see an LMC556 as you mentioned). The LM556 has a supply voltage range of 4.5V-16V. There is a dual package TLC556 (CMOS) that has a supply voltage of 2V-15V. So it looks like your options are to use a single TLC556 (2V-15V supply), or two LMC555s (1.5V-15V). 

For your design, these timers are level sensitive, not edge triggered. Your buttons may need to be switches in order to hold the voltage level. Another option is to attach the output of your button to the clock of a D Flip-Flop so that when your button is pressed, the output of the D-FF will be held at high or low voltage. What is the difference of your RESET button 1/2 from the STOP (second push of Button 1/2)? I believe you can configure the timers in astable mode with a 50% duty cycle, and use the timer reset pin as your start and stop. When the reset pin is held low the output will be low, when reset is held high the timer operates as designed. In the dual packages, each timer has its own reset pin. 

Best,

Katlynne Jones

Hi Andrew,

TI also offers the TLC552, a dual timer in the TLC555/556 family. It is rated for a minimum supply of 1V and uses the same pinout as the TLC556.

https://www.ti.com/lit/ds/symlink/tlc552.pdf

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Kathryn, 

First of all thank you so much for replying . I see that you have a Welsh last name . The TLC556 might be an option ,using on/off switches and a reset button would be possible with level sensitive switching rather than edge triggered . I'm trying to keep the cost down , thus eliminating the D Type flip flops. But more important I'm trying to make the P.C.B as small ( Not surface mount components ) as possible . If you have any application circuits incorporating the components to complete my project I would be most grateful as I'm a novice, but I can solder well .

Kindest Regards 

Andrew 

Dear Thomas 

First of all thank you for replying , much appreciated .

The TLC556 was suggested but the TLC552 .

Does the TLC552 incoprate D type flip flops for Edge triggering or would be better if I just used ON / OFF switchers and a RESET button ?

I'm trying to keep the cost down , thus eliminating the D Type flip flops. But more important I'm trying to make the P.C.B as small ( Not surface mount components ) as possible . If you have any application circuits incorporating the components to complete my project I would be most grateful as I'm a novice, but I can solder well .

Kindest Regards 

Andrew 

Hi Katelynne ,

I do apologize as my last message stated Kathryn . I'm not wearing my reading glasses this evening ...ooops !!

Hello Andrew,

I'll be honest, I am not on top of the different types of flip-flops as I am the precision analog amplifier products that I cover. The TLC556 and TLC552 datasheets show an RS flip-flop, and a RESET pin. I don't think that is exactly the same function as a D flip-flop. You may have a better idea of their equivalency than I do! But do know that the TLC556 and TLC552 do use the same type of flip-flop circuit.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Andrew,

The TLC552 is still going to be level sensitive like the TLC556. The difference is going to be the lower supply voltage. So either way you're going to need to use on/off switches. I'm attaching a Tina-TI simulation for you. The part number is TLC555 but the operation is going to be the same. You can play around with different combinations of the RA, RB, and C values based on the parts you have available to you. The equations necessary to do so are in the data sheet as well as this FAQ on astable 555 timers. In the simulation I have the timer set up in an astable configuration with a period of 60 seconds, 50% duty cycle (so 30 seconds on/30 seconds off). You can attach any LED you have at the output pin of the timer. Just make sure to limit the current with a resistor. 

As you can see in the screenshot of the simulation, when the switch is open (connected to VDD) the timer is tuned on. The timer turns off when you close the switch (connected to ground). The switch can be configured in the opposite way if you would like. One thing to note is that the first high pulse is going to be greater than 30s. This is because the capacitor is charging up from zero as can be seen in the simulation. The FAQ that I linked also provides a solution for this if that is important to you. To get the 30 minute circuit, you would duplicate the 30 second circuit but with different values for RA, RB and C.

I am still wondering what your reset button is doing. How does it different from the on/off functionality of buttons 1 & 2? 

Best,

Katlynne Jones

e2e_Andrew.TSC

Hi Katlynne ,

Thank you once again . Thinking about it I would not need a reset a button as you suggested . AN on/off button for the 30 seconds timer and an on/off button for the 30 minute timer .  I'm hoping an ordinary 1.5 volt battery could power the circuit . I would use miniature L.E.D' s . As you know I'm trying to make the circuit as small as possible with discrete components that I can can put onto veraboard and then hopefully make a little printed circuit board . You mentioned about making the circuit using a computer program called spice . I don't have this program . If you have this software is it possible to make the circuit with software with a glimpse of the inputs and outputs working ? or screen shots .It's a simulation packet if I'm correct .

I'm so grateful for help you have certainly inspired me . This may sound like a silly question if button 1 ( 30s timer ) and button 2 ( 30 minutes) will one Timer work independently from the other or can you get both to work at the same time or either or . The user decides .

Thank you once again .

Kindest Regards

Andrew 

Hi Katlynne ,

Thank you once again . Thinking about it I would not need a reset a button as you suggested . AN on/off button for the 30 seconds timer and an on/off button for the 30 minute timer .  I'm hoping an ordinary 1.5 volt battery could power the circuit . I would use miniature L.E.D' s . As you know I'm trying to make the circuit as small as possible with discrete components that I can can put onto veraboard and then hopefully make a little printed circuit board . You mentioned about making the circuit using a computer program called spice . I don't have this program . If you have this software is it possible to make the circuit with software with a glimpse of the inputs and outputs working ? or screen shots .It's a simulation packet if I'm correct .

I'm so grateful for help you have certainly inspired me . This may sound like a silly question if button 1 ( 30s timer ) and button 2 ( 30 minutes) will one Timer work independently from the other or can you get both to work at the same time or either or . The user decides .

Hi Katlynne  ...... I have downloaded the Tina Simulation Software , never used this before so I'm looking forward to practicing . So the TLC556  atable operation is what I'm going to choose from the library . I guess I select 555 timer from the menu and then enter TLC556 and work around that with VDD which will have a supply of 1.5 volts in my case an then add the ground rail and insert the resistors and capacitors and switches . I'll use a 1 Kohm resisitor to limit the current to the L.E.D'S . 

Thank you once again .

Kindest Regards

Andrew 

Hi Andrew,

I have linked my Tina- TI simulation. You can download it and use the one I have made for you.

3326.e2e_Andrew.TSC

I changed the schematic slightly from the one I posted before. This one has the switch in a different place. The 2 switches will work separately button1 will control the 30 second timer and button2 will control the 30 minute timer. You can choose to use one switch to operate both if you want, but you cant change that after you make your pcb. I don't think the Tina-TI TLC556 model shows the dual timers, so you would just have to use two (the real parts has them both in one chip). Also remember that the TLC556 minimum supply is 2V. So if you do want to supply with 1.5V then you would need to choose the TLC552 like Tom suggested. They all work the same for the most part and for your purposes I don't think the difference matters besides the supply voltages.

Tina-TI is great for simulating circuits before making them on a breadboard. There are a lot of tutorials on TI.com and YouTube if you need help. In your case you will want to run transient simulations to see how the timer is working over time. 

Best,

Katlynne Jones

Hi Katelynne ,

Thank you once again . You mentioned that when Button 1 is open the 30 second pulse would run longer than 30 seconds because of the capacitor charging , do you know much more time ? also thinking about the on / off buttons configured in the opposite way maybe better, as the use presses the button down the LED would light up ..a little more than 30 seconds as you stated before the pulses stabilized at roughly 30 seconds switching on and off .

Once you have constructed the circuit using the Tina Simulation program what do you press in order see the LED go on and off  and the wave forms etc ??

The simulation output .

Thank you once again 

Kindest Regards

Andrew 

Hi Andrew,

I'm attaching a screenshot of the last schematic I made for you. It fixes the longer first pulse problem. When the switch is closed the timer is turned off. At 200s on my simulation you can see that the timer is quickly turned off and then back on (switch closes then opens). 

On/off is relative to the button you're using. You can buy buttons that are push to break rather than push to make. But remember, for this to work without adding D Flip Flops, the button needs to be held in the on position or off position while you want the timer to be operating or not operating. Have you already purchased a button? I would recommend using a slide switch instead. This configuration is a clever way to fix the longer first pulse problem without adding a lot of extra parts. If you do want the switch to work the other way and you want to solve the longer first pulse problem, you would need to use something like Figure 16 in the astable FAQ (which adds an extra transistor and diodes) where reset would be the switch you are controlling. This FAQ explains how much longer the first pulse will be (59% longer) and gives suggestions on how to fix it.

To get the simulation to run you select Analysis and preform a transient simulation. You will not see the LED light up, but in the simulation you can view the voltage at the LED by adding a voltage meter which will let you know if it's on or off. This Tina-TI training series can help you if you need more help with simulations. Make sure to use a Time-Controlled Switch to act as your on/off button. You can double click on the switch and select when you want the switch to be opened or closed. When you run the transient simulation, the switch will be open/closed at the times you selected. 

Best,

Katlynne Jones

Hi Andrew,

I'm attaching a screenshot of the last schematic I made for you. It fixes the longer first pulse problem. When the switch is closed the timer is turned off. At 200s on my simulation you can see that the timer is quickly turned off and then back on (switch closes then opens). 

e2e_Andrew_v1.TSC

On/off is relative to the button you're using. You can buy buttons that are push to break rather than push to make. But remember, for this to work without adding D Flip Flops, the button needs to be held in the on position or off position while you want the timer to be operating or not operating. Have you already purchased a button? I would recommend using a slide switch instead. This configuration is a clever way to fix the longer first pulse problem without adding a lot of extra parts. If you do want the switch to work the other way and you want to solve the longer first pulse problem, you would need to use something like Figure 16 in the astable FAQ (which adds an extra transistor and diodes) where reset would be the switch you are controlling. This FAQ explains how much longer the first pulse will be (59% longer) and gives suggestions on how to fix it.

To get the simulation to run you select Analysis and preform a transient simulation. You will not see the LED light up, but in the simulation you can view the voltage at the LED by adding a voltage meter which will let you know if it's on or off. This Tina-TI training series can help you if you need more help with simulations. Make sure to use a Time-Controlled Switch to act as your on/off button. You can double click on the switch and select when you want the switch to be opened or closed. When you run the transient simulation, the switch will be open/closed at the times you selected. 

Best,

Katlynne Jones